Start injecting TextPane dependencies.

Bundle them up in a static class to avoid having to pass a million deps
around in each and every subclass.

Change-Id: I581e39f9da6f7a4b79ab69d043de4c81111e9b52
Reviewed-on: http://gerrit.dmdirc.com/3064
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager