Added data to companies and modified map view

Added revenue and number of employees to companies (migration and views).
Changed the map to load company category dynamically.
Changed Gemfile to pull Twitter gem from Github
Updated docs with migration info
Added 3 customers to companies. Added migration and updated the views.

Each customer consists of a name and an optional url.
Added checkboxes to map view
Added backend to make map checkboxes work and some minor feedback changes.

Added the backend so category selection on the map now works.
Reordered the elements on the map checkboxes to <checkbox><text><icon>
Added another $ character to the revenue ranges on the company page
CSS fix and added line breaks between customers on the company page

Took desktop.css from production and overwrote the staging one. This fixes the header where "people" is on top of "weWorkInPhilly"
Changed company icon, minor text change on company edit page and added seperators on the map for the different categories.