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.

This is required by the plugins change.

Issue #213

Not sure why we went for String arrays - all lines have a timestamp
and some text. Store this sensibly.

Returning null is bad.

Make Raw optional, mark some fields as @Nonnull.

Doesn't really need to be there, makes more sense as a separate
observer which can do its own thing.

These are absent when disconnected, so use optional instead of null.

Left most of the calls as-is - if something assumed parser was
non-null before it assumes the optional is present now. Should be
easier to clean up later.

- Only show each event once, don't propagate to servers.
- Use a setting to control whether it's enabled or not.

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.