Support both command and GUI

[ghost]

Now lurch can only be controlled with commands, since it should support the client without GUI (eg. finch) according to README.md. But it is not so convenience for normal user who are under GUI. For example, one of the issue is that the notification for OMEMO mode is not so obviously in window title.

I have no idea if it is possible to support both command line and GUI. If it is possible, and implemented, it will be a great improvement for UX.

[ghost]

Just checked "UI requirement: field for PurplePluginInfo and find it looks like not possible to support both pidgin ("PIDGIN_PLUGIN_TYPE") and finch ("FINCH_PLUGIN_TYPE"). That is the same what we got from pidgin-otr - it support pidgin but not finch and libpurple command line.

But after a quick review for pidgin-otr code, I found they introduced "USING_GTK" variable to control the plugin type at the building procedure. I think maybe we can do that in lurch too.

[EionRobb]

@wnereiz you could also create a separate UI plugin that loads the libpurple plugin and sends it the commands so that you don't have to type them

[ghost]

@EionRobb Thanks for the suggestion. But I think what most user need is not only to 'click menu' to execute the commands, but also to get the OMEMO status from GUI which should be obviously. And I hope there should have a 'one-step' solution to avoid install multiple plugins.