Fixes #2615

Attributes of unrecognized tags were being lost
during xml to html translation.
Fixes #2199
Fixes placing of the alt and title attributes in gallery_view template (related: #2185)
Updates translation, fixes #2185
Fixes #2491 - additional rules for basic text correction

Handling some cases of "l"s and "o"s OCR'ed as ones and zeros.
Fixes #2167

Ignoring right alt properly. On Windows this requires
handling two separate key events, the second one (17) being
for ctrl.
Fixes #2061
Reverting unnecessary change (related: #2199)
Fixes #1561
Fixes #1539
Fixes #1598
Fixes #1542
Bringing back yellow background for a fragment wrapped by an unknown tag

Yellow background was accidentally lost in c73940c1babe80cf7a6dd46854dca1543905ae7a
Introducing html/xml transformation tests
Changing test name for clearer reporting
README.md update - tests
Introducing integration tests

$ TEST_BROWSER=Chrome python redakcja/manage.py test --settings settings.selenium tests/integration/
Missing requirement in requirements-test.txt
Updating toolbar/fixtures/initial_data.yaml

initial_data.yaml now contains the result of

$ python redakcja/manage.py dumpdata --format=yaml --indent 4 toolbar

plus change from abc338b9ab6cf47a0b70f8a3f2343bb7b2a5537b