Removed warnings for tight_layout (get rid sooner or later!)
And another environment update (pyFFTW now again accessible via conda!)

dataset: plot_mask now takes kwargs.
fielddata: pad now allows mode changes.
phasemap: fixed bug that did not properly scale vmin and vmax with unit.
io_vectordata: added support for .vtk, .tec files and new interpolation.

environment.yml: upgraded to scipy=1.0

Changed gitlab-ci.yml to use pip install -r requirments.txt instead
(which installes EVERYTHING!)

Added environment.yml and requirement.txt.
GitLab should now produce html coverage artifacts.
io_vectordata: now warns if grid spacing is not equal in all directions.