More gradle/idea fiddling.

Force project name to 'dmdirc'. Think this was the cause of all
the nonsense.

Also add plugins in the root project, so gradle knows about all
of them (for tests etc).

Change-Id: Ic828cabe97040d2ba6cae9336392525ee6bad47c
Reviewed-on: http://gerrit.dmdirc.com/3934
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>