EventUtil tidying.

Move to util package. Add constants for standard priorities.

Change-Id: Id469276751d8a31f19690469540d2c5d07cbe3bc
Reviewed-on: http://gerrit.dmdirc.com/3827
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager
Update submodules: plugins (new commits)

plugins:
    91f3217 Chris Smith <chris@dmdirc.com>
            Handle EventUtil move.

            Depends-On: Id469276751d8a31f19690469540d2c5d07cbe3bc
            Gerrit: http://gerrit.dmdirc.com/3828

Change-Id: Iff1f804633d041fe95ff5fe56f8d62b0e5c0e570
Update submodules: plugins (new commits)

plugins:
    931b474 Greg Holmes <greg@dmdirc.com>
            Invert some ifs.

            Gerrit: http://gerrit.dmdirc.com/3826

Change-Id: Idcea11140e2db3a097b0a1c6e300a2b886f5bbdc