New toolbar style.

This includes:

- Button label is now hidden by default. Shows as tooltip on hover.
- No "button"-look any more for toolbar buttons.
- Overall slimmer toolbar.
- New link, button and input focus style.
Put an insert element button between and above each element.

Before we had one button that always appends the element at the end of the list.
Now the user can choose where to add the element.
Stick RSpec to version 2.x

RSpec 3.0 has just been released. Since they use a new syntax now, many
tests broke. For the time being, stick RSpec to the latest 2.x version, no? :)

Thanks, and keep up the good work :)
Remove Alchemy::Page's dependency to have the user extend ActiveModel
Rename Alchemy::Page model concerns to avoid namespace conflicts
Bump version to 3.0.0.rc6
Merge commits from original repository