[renderer] Removed cairomm

Cairomm is unmaintained and there are serveral unfixed bugs. Since I
don't want to maintain cairomm myself, we switch to plain C cairo.
[renderer] Remove MetaTile and add RenderCanvas

Every thread now gets a set of RenderCanvas objects that are persistent
over rendering runs.
[build] Removed Cairomm and SigC++ from cmake
[tests] Fixed test compilation.
[build] Removed cairomm from travis
[build] Add Sanitize build type
[importer] Remove way type precomputation
[tests] Only generate valid ways/relations
Merge pull request #47 from alacarte-maps/cairomm-removal

Cairomm removal