Update submodules: plugins (new commits)

plugins:
    ca61346 Greg Holmes <greg@dmdirc.com>
            Tidy up TreeTreeScroller.

            Gerrit: http://gerrit.dmdirc.com/3678

Change-Id: Ib226edbd46dc3eeb9466ea70b0522918f02ace04
Add project files for IDEA

Change-Id: I951f5827472d9a91e3426933c2d5b05fc722f0af
Reviewed-on: http://gerrit.dmdirc.com/3679
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>