Style Attributes Content Handler

This pull request is for a new common content handler that we have developed at Constant Contact.

The Style Attribute Content Handler will remove all unsupported style attribute items from all elements in the supplied content.  The set of supported style attribute items is configured in the same manner as other content handler plugins via config in 
```
Aloha.settings.contentHandler.handler.styleattribute.
```
This code has been tested across browsers by our QE and is used in our product.

1. obey coding guidelines
2. write JSLint compliant code
3. write JSDoc for every method you touched during your implementation
4. write a human-readable :) Changelog entry that describes your change
5. add a qunit test (if it makes sense) and/or document the steps to manually test it (in a separate guides page)
6. test your changes in Internet Explorer 7, 8, 9 and the latest Firefox and latest Chrome
7. document your changes in a guides page
8. include this list in a your pull request