refactor(dialog): remove deprecated content options and methods

BREAKING CHANGE: Removed support for the deprecated `.content('string')` methods and options. These were deprecated in favor of `.textContent('string')` and `.htmlContent('sanitized-string')'` methods and their associated options. Please note that use of `.htmlContent` requires that the `ngSanitize` module be loaded.

If you have
```js
  alert = $mdDialog.alert()
    .content('This is an example.');
```
It needs to be changed to
```js
  alert = $mdDialog.alert()
    .textContent('This is an example.');
```
If you have
```js
  alert = $mdDialog.alert({
    content: 'This is an example.'
  });
```
It needs to be changed to
```js
  alert = $mdDialog.alert({
    textContent: 'This is an example.'
  });
```

src/components/dialog/dialog.js

@@ -561,17 +561,17 @@ function MdDialogProvider($$interimElementProvider) {
       options: dialogDefaultOptions
     })
     .addPreset('alert', {
-      methods: ['title', 'htmlContent', 'textContent', 'content', 'ariaLabel', 'ok', 'theme',
+      methods: ['title', 'htmlContent', 'textContent', 'ariaLabel', 'ok', 'theme',
           'css'],
       options: advancedDialogOptions
     })
     .addPreset('confirm', {
-      methods: ['title', 'htmlContent', 'textContent', 'content', 'ariaLabel', 'ok', 'cancel',
+      methods: ['title', 'htmlContent', 'textContent', 'ariaLabel', 'ok', 'cancel',
           'theme', 'css'],
       options: advancedDialogOptions
     })
     .addPreset('prompt', {
-      methods: ['title', 'htmlContent', 'textContent', 'initialValue', 'content', 'placeholder', 'ariaLabel',
+      methods: ['title', 'htmlContent', 'textContent', 'initialValue', 'placeholder', 'ariaLabel',
           'ok', 'cancel', 'theme', 'css', 'required'],
       options: advancedDialogOptions
     });
@@ -698,8 +698,7 @@ function MdDialogProvider($$interimElementProvider) {
 
       if (controller) {
         var mdHtmlContent = controller.htmlContent || options.htmlContent || '';
-        var mdTextContent = controller.textContent || options.textContent ||
-            controller.content || options.content || '';
+        var mdTextContent = controller.textContent || options.textContent || '';
 
         if (mdHtmlContent && !$injector.has('$sanitize')) {
           throw Error('The ngSanitize module must be loaded in order to use htmlContent.');
@@ -741,8 +740,7 @@ function MdDialogProvider($$interimElementProvider) {
         });
 
       /**
-       * For alerts, focus on content... otherwise focus on
-       * the close button (or equivalent)
+       * For alerts, focus on content... otherwise focus on the close button (or equivalent)
        */
       function focusOnOpen() {
         if (options.focusOnOpen) {

src/components/dialog/dialog.spec.js

@@ -33,8 +33,7 @@ describe('$mdDialog', function() {
 
   describe('#alert()', function() {
     hasConfigurationMethods('alert', [
-      'title', 'htmlContent', 'textContent', 'ariaLabel',
-      'ok', 'targetEvent', 'theme'
+      'title', 'htmlContent', 'textContent', 'ariaLabel', 'ok', 'targetEvent', 'theme'
     ]);
 
     it('shows a basic confirm dialog without content', inject(function($animate, $rootScope, $mdDialog) {
@@ -342,8 +341,7 @@ describe('$mdDialog', function() {
 
   describe('#confirm()', function() {
     hasConfigurationMethods('confirm', [
-      'title', 'htmlContent', 'textContent', 'ariaLabel',
-      'ok', 'cancel', 'targetEvent', 'theme'
+      'title', 'htmlContent', 'textContent', 'ariaLabel', 'ok', 'cancel', 'targetEvent', 'theme'
     ]);
 
     it('shows a basic confirm dialog with simple text content', inject(function($rootScope, $mdDialog) {
@@ -405,26 +403,6 @@ describe('$mdDialog', function() {
       expect(content.text()).toBe('Choose');
     }));
 
-    it('should support the deprecated `content` method as text', inject(function($mdDialog) {
-      var parent = angular.element('<div>');
-
-      $mdDialog.show(
-        $mdDialog.confirm({
-          parent: parent,
-          ok: 'Next',
-          cancel: 'Back',
-          title: 'Which Way ',
-          content: '<div class="mine">Choose</div>'
-        })
-      );
-
-      runAnimation();
-
-      var contentBody = parent[0].querySelector('.md-dialog-content-body');
-
-      expect(contentBody.textContent).toBe('<div class="mine">Choose</div>');
-    }));
-
     it('should NOT allow custom elements in confirm htmlContent', inject(function($mdDialog) {
       var parent = angular.element('<div>');
 
@@ -674,7 +652,7 @@ describe('$mdDialog', function() {
 
   describe('#prompt()', function() {
     hasConfigurationMethods('prompt', ['title', 'htmlContent', 'textContent',
-      'content', 'placeholder', 'ariaLabel', 'ok', 'cancel', 'theme', 'css'
+      'placeholder', 'ariaLabel', 'ok', 'cancel', 'theme', 'css'
     ]);
 
     it('shows a basic prompt dialog', inject(function($animate, $rootScope, $mdDialog) {