Move AliasDialogModelAdapter to core.  Add check for current alias.

Change-Id: Ic547ed6e12879c7c6ea77d2c6766989c01dff640
Depends-On: I71d77d5c76f72e44303d2fd7f5dede75eef89ec1
Reviewed-on: http://gerrit.dmdirc.com/3580
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>