IMAP: Add wp-cli module

[r-a-y]

If the auto-connect option is off, IMAP connections are currently initiated on a pageload and uses some filemarkers to determine if an IMAP connection is active or not. This method has limitations (see #56 for more background info).

One way to address this is to write a wp-cli module so if IMAP mode is selected, it can run on its own background process that will not rely on the current pageload method.