Change registration button based on number of modes.
Add new column to CourseMode table for currencies
Add in tests for the marketing site button.
updated styling for marketing side register button to accommodate second line of text
updated styling for marketing side register button to accommodate second line of text - and IE-specific styling
Add in a uniqueness constraint on mode, course, and currency.
mktg - revised sass/css for iframed button to match styles/consistency
Merge pull request #713 from edx/diana/button-updates

Drupal side Register button updates