add initial_croppings on pre_save
do not crash when using invalid images (e.g. pdf renamed to jpg)
tests for initial cropping
fix test for python3
Merge pull request #49 from jonasundderwolf/feature/initial_cropping

Feature/initial cropping
Move screenshot in README further up
Bump version
Remove runtests script and rather use tox all along the way
Use xpath when looking for elements in selenium tests
Rather wait implicitly
Try to work around timeout issues on Travis CI
Merge branch 'tests' into tox-travis

Conflicts:
	example/requirements.txt
	example/tests/test_browser.py
Merge branch 'tox-travis' into next

Conflicts:
	example/tests/test_browser.py
	tox.ini