Constrain Matplotlib dependencies to pyPlots submodule

[alhom]

For example, pyCalculations depends on cbfmtsci for formatting strings, which resides in pyPlots (... which import matplotlib), see e.g. here:

analysator/analysator/pyCalculations/variable.py

Line 26 in 380989e

from plot import cbfmtsci

This issue might be mitigated by implementing lazy loading (#351).

[alhom]

The above from plot import cbfmtsci import still triggers matplotlib import when not really needed.

#361 has reduced impact because of that.