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.