wxGUI: Add the ProjPicker page to the Location Wizard (Continutation)

[ocsmit]

This pull request is a continuation of the work of #1770 in addressing #1253 to add a location wizard which is spatially queryable.

The goals/scope of the continuation are

• Inclusion of toolbar for users. ¹
• Smoother OSM map loading (e.g. lazy loading, separate thread, ...). ²
• Merge with standard EPSG search wizard. ²

@HuidaeCho Feel free to add anything I missed!

[HuidaeCho]

Flake8 is happy with

l, r = 1, 2

but not with

l, O = 1, 2

and

l = 1
r = 2

Inconsistency... As a result, we have inconsistent naming.

• l, r, t, b
• le, ri, to, bo
• left, right, top, bottom
• n, s, w, e
• north, south, west, east

Many short variable names fail Pylint testing because this new module is not excluded from .pylintrc.

[HuidaeCho]

Working on pylint...