This introduces a CachingDocument which wraps around an IRCDocument
and allows UI-specific caching of UI-specific styled lines (so, e.g.
the web UI could cache HTML versions if it wanted).

Also adds a delegating message maker and attributed string maker,
which incorporates the old "make a StyledDoc then change it into
an AttributedString" logic found in ui.core.util.Utils.

Hopefully this should mean all the the swing stuff can be punted
into the swing UI. The delegated maker will also allow colouring
of the new events to be done sensibly, I think.

Put it behind a nice interface, so the styliser can work without it
and be tested, and other UIs don't have to use swing junk.

Returning null is bad.

Change-Id: I0bb97a8946d1c217de82fe2a9b8f35b7d49eae06

It doesn't really make sense in ui.core now it's doing more...
The classes it's integrating are all in messages.

Urgh.

Closes #156

Remove existing auto commands dialog model.

These should really only be accessed through a ConfigManager.

Remove some pointless setup from WritableFrameContainerTest.