Formatting and fixes

* Moved: some existing functions into new separate files to improve code
readability (detailed in __init__.py docstring)

* Remove: max_intersections deprecated in pov 3.8

* Add: Validate utf-8 characters with specific API function at session's
first script init

* Add : Icons to some text fields and inviting labels

* Change default camera normal perturbation value to non zero since its
use is first driven by a boolean toggle

* Change: lists (vectors and indices) are now exported in one line by
default for better manual scene overview and debugging

* Change: a couple of tooltips corrections

* Change : renamed many variables and functions to snake_case according
to recommanded style guides

* Fix : Heightfield primitive (forward slashes were expected for
displacement texture path)

* Fix : Text nippet insertion operator

* Fix : added console print tip to check executable path on failure to
process

* Fix : tweaked finished render say command for Linux

* Fix : interface of some shader nodes broken since 2.8 api changes

* Fix : export hair particles