Some login/signup template updates.
- Customized subject and body when inviting users to a league.
- Slug creation for leagues is now robust.
Minor changes to login related forms templates.
Merge pull request #17 from nessita/invite-improvemtns

Customized subject and body when inviting users to a league.
Minor css updates.
Minor label update.
Merge pull request #18 from matiasb/login-tweaks

Login tweaks
Enabled facebook login button.
Added flatpages app and links for FAQs and rules.
Updated home with in-progress information.
Added 404/500 templates.
Merge pull request #19 from matiasb/rules-and-faqs

Added flatpages support and 400/500 templates.
Updated 404/500 templates.