Add placeholder text for signup form.

Fixes #42
Fixes #53

Changes:
* add jquery-placeholder library for old IE placeholder support
Merge pull request #56 from thegarage/placeholder-text

placeholder-text
remove email_preview gem

Use Rails 4.1 ActionMailer Previews as preferred pattern instead.
use precompiled_css_files helper
Merge pull request #57 from thegarage/remove-email-preview

remove-email-preview
Add default header to layout for public pages.

Fixes #43

Screenshot of default header:
https://www.evernote.com/shard/s7/sh/148ba858-145f-4c0d-993a-e43d873ebd69/ac21b6dccde021406bb06e63a617ff15

Changes:
* Add content_for :header to configure custom header per page
* Update home page to "opt-out" of default header rendering
* combine _navigation and _navigation_links partials into _header
Merge pull request #58 from thegarage/layout-header

layout-header
* added mini-profiler gem
Merge pull request #61 from thegarage/add-mini-profiler

add-mini-profiler
upgrade to ruby 2.1.4

* https://trello.com/c/GKE510lr/382-ruby-2-1-4
Merge branch 'upgrade-ruby'

* upgrade-ruby:
  upgrade to ruby 2.1.4