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.

Issue #750

Issue #424

This will allow the formatter to check if strings coming from
(for example) users in channels should be formatted specially,
such as by colouring or linking them.

Issues #424 and DMDirc/Plugins#507

Our API shouldn't depend on MBassador. Extract a simple interface
to break the dependency.

This is for the interfaces/trivial implementation classes that
DMDirc plugins can interact with. Eventually plugins will build
against the API instead of the DMDirc client itself, which will
allow for remote/detachable clients (amongst other things).