move configuration for test environment into separate file conftest.py

lazy initialization of highlight pens and brushes for DebugVariableViewer

Constructors wx.Pen() and wx.Brush() require wx.App to exist already.
That causes crash during import of the control,
because import is done before calling main application code.

add '_' function to builtin dictionary at import time

This allows to import many Beremiz python modules before calling
util.misc.InstallLocalRessources().

remove builtin BMZ_DBG. It's not used.