Ushahidi Installer

Summary:
* updates the prototype installer with new styles
* Fixes T138

Test Plan:
* load home page with `?install=1` to activate installer
* review layout from M14 feedback
* resize browser for responsive views

Reviewers: shadowhand

Reviewed By: shadowhand

Subscribers: dkobia

Maniphest Tasks: T138

Differential Revision: https://phabricator.ushahidi.com/D234