Bug fixes and new placeholder feature

Few bug fixes:
- Fix 'TypeError: Cannot read property 'length' of undefined' on editValue when it is undefined/null.
- Change the bower.json main tag to be the actual files per the spec at https://github.com/bower/bower.json-spec.  These get leveraged plugins such as grunt-wiredep

New features:
- Add ng-focus to go into edit mode immediately upon receiving focus.  Add tabindex as well so you can tab to different editable-text fields.
- Added ui-keypress to leave edit mode upon receiving enter in the input field.  ui-utils (http://angular-ui.github.io/ui-utils/) is obviously required for this to work.
- Add new placeholder feature, which will show a placeholder in both the display text and input field when the editable value is null.  Example usage: <span editable-text="firstName" placeholder="[First Name]"></span>