Allow the Tooltip target container to have a custom style

Summary:
The target markup is wrapped in a `div` which is a problem if you want
the target markup to be inline with other text.  Add the ability to style
the target markup container to avoid this problem.

Use PropTypes.any

Test Plan:
Use a tooltip and include a `targetContainerStyle` to style the
markup found in the target section

Reviewers: riley

Reviewed By: riley

Differential Revision: https://phabricator.khanacademy.org/D32039

Author: Brian Genisio

examples/tooltip.jsx

@@ -4,6 +4,11 @@ var pStyle = {
     padding: 10,
     backgroundColor: "white"
 };
+
+var tStyle = {
+    display: 'inline-block',
+    fontWeight: 'bold'
+};
 // }}}
 
 return <Tooltip className="class-for-tooltip-contents"
@@ -12,6 +17,7 @@ return <Tooltip className="class-for-tooltip-contents"
                 verticalPosition="bottom"
                 arrowSize={10}
                 borderColor="#ccc"
+                targetContainerStyle={tStyle}
                 show>
     <div>reticulating splines!</div>
     <p style={pStyle}>

js/tooltip.jsx

@@ -24,6 +24,7 @@ var _ = require("underscore");
  *         arrowSize={10} // arrow size in pixels
  *         borderColor="#ccc" // color of the border for the tooltip
  *         show={true} // whether the tooltip should currently be visible
+ *         targetContainerStyle={targetContainerStyle}
  *         >
  *     <TargetElementOfTheTooltip />
  *     <TooltipContents1 />
@@ -216,7 +217,8 @@ var Tooltip = React.createClass({
         ),
         children: React.PropTypes.arrayOf(
             React.PropTypes.element
-        ).isRequired
+        ).isRequired,
+        targetContainerStyle: React.PropTypes.any,  // style object
     },
 
     getDefaultProps: function() {
@@ -226,7 +228,8 @@ var Tooltip = React.createClass({
             borderColor: "#ccc",
             verticalPosition: "bottom",
             horizontalPosition: "left",
-            horizontalAlign: "left"
+            horizontalAlign: "left",
+            targetContainerStyle: {},
         };
     },
 
@@ -250,7 +253,7 @@ var Tooltip = React.createClass({
 
             {/* We wrap our input in a div so that we can put the tooltip in a
                 div above/below it */}
-            <div>
+            <div style={this.props.targetContainerStyle}>
                 {_.first(this.props.children)}
             </div>