lazy locale initialization

wx.Locale() can't be called without wx.App. So don't call it at
import. It makes PLCOpenEditor simpler.

use CustomIntCtrl instead of wx.SpinCtrl because it doesn't support
long integer needed for UDINT, (U)LINT types.

This commit complements commit 74a3f4d "fix LINT and ULINT ranges".

add custom TextCtrl allowed to enter long integer with bounds checking

It's needed because wx.SpinCtrl supports only 'int' type. For UDINT
and (U)LINT long type is necessary.

use pytest for testing

run separate test on every project instead of one big long test all projects

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.