Move imap management to controller class: IS_Inbox_Status
Add __get() convenience method.

If a variable is accessed from outside the IS_Inbox_Status class,
return a value from method get_$var()

For example, $inbox->unread_count returns $inbox->get_unread_count()
Allow plugin HTML output to be overidden by WordPress theme.

Moved Widget HTML into "templates" directory.
Renamed "themes" directory to "templates".