This is horribly icky and wrong. The only place it's used is
PluginFilesHelper, which can easily be given its own manager.

Also fix annoying shaded import.

Alternative highlights were never added because the maps were
optimised away; then the list occasionally ended up with null
entries as they were added concurrently.

Remove them from the Connection interface.

This isn't used in the UI, and doesn't need to exist with the
individual setter methods.

Fixes #280

Stab bits of ignored tests that no longer work.

This adds a sendLine method to Connection, which is a bit icky,
but is useful when the end-user is supplying lines to pass
directly to the underlying connection.

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.

Remove existing auto commands dialog model.

Will write a new wrapper for the new model.