made admin site name customizable via a setting attr
fixed AdminUserModelForm import so it doesn't on custom user model
more elegant way of fixing the import issue
changed the tag to bring in both the name and description
updated documentation to explain new settings attributes
updated documentation to clarify user modelform override
Merge pull request #15 from volksman/master

Added ADMIN_SITE_NAME & ADMIN_SITE_DESCRIPTION settings + fixed potential import problems with the User model form (refs #14)