- GroupChatManager never subscribed to the event bus
- Comparing Optional<Connection> to Connection fails

Closes #782

This allows "unstyled" to actually work.

Closes #755

I'm sure this will be changed/redone, but this is at least a start by allowing
certain events to go to all windows (eg ServerNotices)

Ideally it would be possible for some events to only be displayed in the window
that generated them (eg if I do /notice foo bar the ">-{{target}}-> {{message}}"
message only appears in the window I ran the command in, not either just the
server window or all the windows, but this would need changes to a bunch of
events to make them include a source window.

We now specify the default colour using display properties, not
by ascribing special value to the first colour code in a message.

Closes #741

Issue #750

Issue #750

Issue #750

Closes #755

This won't affect normal use of the client, other than it having
a few extra unused classes and some additional lines in the
manifest.

Issue #750

Closes #757

Issue #753

Closes #751

If an object in a formatter tag ({{foo.bar.baz}}) is Displayable,
then we will modify the output based on its display properties.

Currently only supports user links and foreground colours.

This also changes the internal format of nickname links to be
`\u16<nick to link to>\u16<text to show>\u16`, allowing the
link and text to differ. This means if you formatted users
by showing their realname, you could still click them to
open a query.

Closes #424
Closes DMDirc/Plugins#507

Issue #424

I broke it in my interface-extraction shennanigans.

Closes DMDirc/Plugins#509

Make it extend a list instead of wrapping it, so we can just replace
all usages with... an actual list.

Flip BaseCommand and Command around so everything still works.

Command will eventually become an interface when all usages have been replaced