improved version of `time_profile_at_plane`

should be much faster

update .gitignore and tests, matplotlib workaround

Testing on python:latest using a gitlab docker runner.

Scipy intoduced another paramter for padding, which apparently was zero
before. Fixing this.

The scipy change is:
scipy/scipy@9c299da

Alex noted, that on his implementation, using the normal
map_coordinates function was really slow. (I am guessing due to extra
memory allocation), which is why he called the C-Function directly and
did all the checks within postpic. So keep it as is for really fast
coordinate mapping :)

Fix #261

Scipy intoduced another paramter for padding, which apparently was zero
before. Fixing this.

The scipy change is:
https://github.com/scipy/scipy/commit/9c299da04b9c419786a56c8e657aaabeb35f9069

Alex noted, that on his implementation, using the normal
`map_coordinates` function was really slow. (I am guessing due to extra
memory allocation), which is why he called the C-Function directly and
did all the checks within postpic. So keep it as is for really fast
coordinate mapping :)

Fix #261

* replace Travis badge by github action badge
* add script to create/update gh-pages branch

Docs

set to python 3.8, as 3.9 numpy under macos doesnt work as descirbed here:
https://github.com/numpy/numpy/issues/17550

the mocked function dont seem to have a __name__ attribute. However,
mocking pyfftw fails the doc creation entirely.

Fbpic modeexpansion upgrades. pyfftw is limited to 1 thread to be compatible with multiprocessing.

maintenance

remove atlas dependency
remove unsopported python2.7 (which has failed)
remove versions unsupported by conda

GitHub actions

run test in github-actions. Also allow python2 test to fail due to end of its support.