[TIDOC-1806] Added UI to support filtering by platform

* Changed 'Show' button label to 'Filter' and added filter CSS icon based on feedback (TODO: better align icon in button)
* Added checkboxes to Filter menu for each platform (iOS, Android, Tizen, Mobile Web, Blackberry)
* Linked minified fontawesome CSS file in template.html. This provides the new filter icon.



Capitalize 'Web'.  I think we should alphabetize the names.  We also distinguish between iPhone and iPad in the docs.