Fix dependency problem, and tidy a bit.

Get rid of all the Main.getPluginManager() references.

Change-Id: I2a377ce00423af5c560e0fd840948568d771b566
Reviewed-on: http://gerrit.dmdirc.com/2712
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager