Encapsulate into gem

[fabianrbz]

@mheap this PR encapsulate the app into a gem so it's easier for us to mount it in the Rails app. There are three things that I need to take care of but we could probably do them once we merge and test this. Those are:

• [x] add a proper README, once we are ok with how the gem is being used and included in the rails app
• [x] -there are some filters that have some paths to some views that still point to the rails app-, we should fix those and extract those views to the gem if they are used in both apps
• [x] fix the download links

EDIT: We probably need to add the corresponding git submodules to this repo now

[fabianrbz]

@mheap we need to discuss adding the submodules here and removing them from the rails app.