[server] Render tiles in groups of 4x4
[renderer] Work around broken write-func handling in Cairomm
[job] Fixed prerendering
[statistics] Write statistics to file in bulk.
[request_manager] Added timing for prerendering.
[statistic] Add slicining time to measurement.
[statistic] Fixed initialisation and output
[statistic] Don't crash on shutdown when no performence log was specified
[statistic] Add tool to create bar graphs from performence logs
[statistic] Implement moving average for statistics.
[tests] Get server tests to compile and run again
[tests] Add custom target tests and build input files automatically
[tests] Fixed empty TI test
[cache] Reduce logging output
[renderer] Remove renderTile and instead add renderEmptyTile

Since the whole job scheduling depends on meta tiles it
makes no sense to support both architechtures in the renderer.
[tests] Fixed renderer tests
[cache] Fixed caching of svg images