Update Gemfile to remove unused gems

Removed masonry-jquery from the project as it was not needed any longer.
Added jquery-ui gem for visual improvements on the index page.
Update require statements in css and js

Removed masonry require statements from application.js and
application.css, and added the ones for jquery-ui on both of them.
Updated view, javascript and css of index page

Added support for post pictures grid on initial page. Also updated css
to provide styles not supported by bootstrap.