Refactor projects based on career day feedback

Based on feedback from demo, removed successful projects from projects
index, added success feedback on projects show.

Moved donation levels sorting from controller to model, tidied up
percentage calculation-related code in model.
Remove modal login, fix signup and login partials

Remove bootstrap js modal login, since it turns out bootstrap doesn't
support adding js hooks to buttons within the modal, so I can't add a
"success" action to the login button in the modal. This feature will
have to be added as a later project using a home-made ajax-ified modal.

Move context specific text out of form partial and into respective view
page.

Display user info on user show page, fix typo in page header.
Minor readme updates