[Tilesathome] Improvements all over the place

[Jiri Klement]

> 2) The server locks entries that it is about to hand out to clients in the database now. WHile I had difficulties getting this to work, it does now. So you shouldn't see the same tileset be assigned to multiple clients. This was also a waster of client CPU and API bandwidth, so this would also contribute to increased performance.

Something is still wrong. I get following exception every time I try
to get next request:

Exception Type:	OperationalError
Exception Value:	(1205, 'Lock wait timeout exceeded; try restarting
transaction')