Replace IMAP class with PEAR Net_IMAP

This removes dependencies on PHP's IMAP extension.

Some hosts may not include the IMAP extension,
or may not compile it with SSL, which is needed for Gmail.
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".
Disable front-end JS. Move __get() next to __construct().
Add unread-emails and total-emails shortcodes
Add actions for template output.

Usage:

```
do_action( 'inbox_status_unread_count' );
do_action( 'inbox_status_total_count' );
```
Fix textdomain in PHP error.