PySection: adopt to nix property / value redesign

This commit fixes some issues with compatibility to
nix intruduced by nix/#292.

This partially resolves #50.
PyDataArray: function naming conventions
PyDataArray: adopt to changed data array creation

Adopt PyDataArray to changes introduced by nix/#299
This coveres partially #50 and #51
data_array.py: remove create data method

Adopt to changes made for fixing nix/#293
test: fix all tests

Adopt to changes made for fixing nix/#293 and nix/#220

This fixes #50 and #51
PyBlock: fix issue with createDataArray overload
Merge pull request #52 from stoewer/master

Adopt to changes introduced to the nix API

LGTM!