Annotation Based Discussions

Added a feature to enable discussions based on some selected text.
- Currently, works for pages, files and groups.
- To enter annotation mode either click on the Annotate icon or select some text. 
- Select text to add annotations.
-Your selection shall be automatically extended to include entire words.
- To view already existing comments, click on the respective text (shown in different color).
- Annotations on overlapping text are allowed.  
- To exit the annotation mode, click on the Annotate icon.
- To ensure proper working of the code, please ensure that bower is installed.