Simple drawing tests for Image backend.
Merge branch 'feature/abstract-graphics-context' into template-test-case-for-graphic-contexts
make the tests folder a subpackage
add a test template for drawing with graphic contexts
add tests for the agg GC
add tests for the pdf GC
add tests for the QPainter GC
remove old testcase
split a special tester subclass for gui toolkit related contexts
use the DrawingImageTester
support some very basic testing for the PDF backend
update tests about agg drawing
provide just the name without the extension in self.filename
add tests for the ps backend
update the pdf tests
add basic drawing tests for svg
add workaround for and ps, svg tests to function
add testcase for the gl backend
minor cleanup
add tests for the cairo backend