Add doc about how to customize navbar
Branch: bug/296-navbar
Allow for customizing nav bar more
Branch: bug/296-navbar
Refs #296: more style changes to navbar

- make the words in the responsive menu white on blue instead of gray on blue
- change the responsive menu button from solid black to a gradient to the same
  shade of blue used elsewhere.

Branch: bug/296-navbar
Refs #295: Login and other forms use Bootstrap

- modify render_form tag to use Bootstrap-style markup when rendering a form
- modify login page to use render_form tag and other Bootstrap markup

Branch: 295-style-login-form
Merge pull request #296 from rapidsms/bug/296-navbar

Customize and clean up navbar
Merge pull request #295 from rapidsms/295-style-login-form

Style the login form
Refs #294: Make main-page top padding conditional

Make the main-page top paddding conditional on being above the largest
responsive breakpoint. Once we get down to the breakpoint, it seems
unneeded and we had way too much top padding.

Branch: feature/294-headers
Merge branch 'release-0.12.0' into feature/294-headers

Branch: feature/294-headers