[GSOC-UPDATE](19.07) Impress Remote

[Andrzej J. R. Hunt]

Hi everyone,

I made some good progress today:

- Finally found and fixed the cause of segfaults in the Transmitter 
(thanks to Valgrind).
- Fixed some problems with the Listener lifecycle.
- Fixed the listening loop in the Server to properly exit when the 
connection is closed.
- Fixed listener registration for the case where a client connects 
before a slideshow starts.
- Refactored the image preview code to send all images to the client 
when a slideshow starts.
- All the above mean that communication from server to client is now 
reliable, and the current slide preview is shown on the app / updates 
with the presentation.

This means that tomorrow I should be able to start work on the various 
views for the app!

Cheers,
Andrzej