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.
Companies with multiple categories now supported.

Changed the company model to return all categories instead of just one to the mapfeed.
Changed the javascript for the map to display a company when any of its categories are checked. Will always display the first category (in order entered in the tags) that is checked.
Various medium priority bonus changes/additions

Added a url parameter "loc". The map will scan for this parameter and only display companies with an address containing the value.
Added contributors Chris Cera, Brad Oyler, and Andrew Scott.
Fixed a bug in the map that caused broken links to be displayed.
Added a "Jobs Page" url to companies that gets displayed on the map.
Added category filtering to the map widget.
Added groups to the map and various minor UI edits.

Groups now have addresses and are displayed to the map if they have an address.
The category checkboxes are now above the map widget.
Changed the "brought to you by" link.
Changed the map header.
Added Contributors.md
Added option to not display categories on map widget and minor footer change.
Added/changed the "Get a job here" link and updated map widget to not initialize twice.
Implemented stakeholder feedback.

Removed events from categories.
Changed organizations icon.
Changed categories from tags to checkboxes.
Changed revenue and number of employees to dropdowns.
Moved the map link.
Changed map category default from company to startup.
Documentation updates (intermediate).
README now contains latest developer documentation