fix(filterRow.html): header-class should also apply to filter row

BREAKING CHANGE:

A css class specified using the header-class will now be added to the filter row header cell and not
just the sorting row.

If you want to continue to apply the css rules *only* to the cell in the sorting header row you
will now need to qualify your css rule with the '.header' css class.

So the following:

```css
.my-customer-header {
    /* rules */
}
```

... will need to change to:

```css
.header.my-customer-header {
    /* rules */
}
```

src/ng-table/filterRow.html

@@ -1,5 +1,5 @@
 <tr ng-show="show_filter" class="ng-table-filters">
-    <th data-title-text="{{$column.titleAlt(this) || $column.title(this)}}" ng-repeat="$column in $columns" ng-if="$column.show(this)" class="filter"
+    <th data-title-text="{{$column.titleAlt(this) || $column.title(this)}}" ng-repeat="$column in $columns" ng-if="$column.show(this)" class="filter {{$column.class(this)}}"
         ng-class="params.settings().filterOptions.filterLayout === 'horizontal' ? 'filter-horizontal' : ''">
         <div ng-repeat="(name, filter) in $column.filter(this)" ng-include="config.getTemplateUrl(filter)" class="filter-cell"
              ng-class="[getFilterCellCss($column.filter(this), params.settings().filterOptions.filterLayout), $last ? 'last' : '']">

test/tableSpec.js

@@ -139,17 +139,28 @@ describe('ng-table', function() {
             var rows = thead.find('tr');
             var titles = angular.element(rows[0]).find('th');
 
-            expect(angular.element(titles[0]).hasClass('header')).toBeTruthy();
-            expect(angular.element(titles[1]).hasClass('header')).toBeTruthy();
-            expect(angular.element(titles[2]).hasClass('header')).toBeTruthy();
+            expect(angular.element(titles[0]).hasClass('header')).toBe(true);
+            expect(angular.element(titles[1]).hasClass('header')).toBe(true);
+            expect(angular.element(titles[2]).hasClass('header')).toBe(true);
 
-            expect(angular.element(titles[0]).hasClass('sortable')).toBeTruthy();
-            expect(angular.element(titles[1]).hasClass('sortable')).toBeTruthy();
-            expect(angular.element(titles[2]).hasClass('sortable')).toBeFalsy();
+            expect(angular.element(titles[0]).hasClass('sortable')).toBe(true);
+            expect(angular.element(titles[1]).hasClass('sortable')).toBe(true);
+            expect(angular.element(titles[2]).hasClass('sortable')).toBe(false);
 
-            expect(angular.element(titles[0]).hasClass('customClass')).toBeTruthy();
-            expect(angular.element(titles[1]).hasClass('customClass')).toBeTruthy();
-            expect(angular.element(titles[2]).hasClass('moneyHeaderClass')).toBeTruthy();
+            expect(angular.element(titles[0]).hasClass('customClass')).toBe(true);
+            expect(angular.element(titles[1]).hasClass('customClass')).toBe(true);
+            expect(angular.element(titles[2]).hasClass('moneyHeaderClass')).toBe(true);
+
+
+            var filterCells = angular.element(rows[1]).find('th');
+
+            expect(angular.element(filterCells[0]).hasClass('filter')).toBe(true);
+            expect(angular.element(filterCells[1]).hasClass('filter')).toBe(true);
+            expect(angular.element(filterCells[2]).hasClass('filter')).toBe(true);
+
+            expect(angular.element(filterCells[0]).hasClass('customClass')).toBe(true);
+            expect(angular.element(filterCells[1]).hasClass('customClass')).toBe(true);
+            expect(angular.element(filterCells[2]).hasClass('moneyHeaderClass')).toBe(true);
         });
 
         it('should create table header titles', function() {