HH-43961 improve tests
HH-40165 add preprocessors
HH-40165 update docs and misc
Merge remote-tracking branch 'origin/HH-43961' into EXP-11504
Merge remote-tracking branch 'origin/HH-40165' into EXP-11504
release 2.20.0 [an.sumin@hh.ru]
new debug with Jinja2
make logging more consistent
new stages, log request_time instead of app total time
add tests for debug page
add coverage to tests run
improve frontik.testing
drop python 2.6
add new tests