Improve selection table in python UI dialog

[tamarinvs19]

Description

• New table which can show python classes and python functions
• Support for choosing python classes and functions in Project window include from directory and from selected files

Fixes #1569
Fixes #2128

How to test

Manual tests

Classes

1. Try to generate tests from file with one or more classes (click utbot combination not inside class)
2. Expected: class check boxes in dialog

Classes and functions

1. Try to generate tests from file with one or more classes and one or more functions (click utbot combination outside all code objects)
2. Expected: class check boxes and function check boxes in dialog

Generation from Project

Try to generate tests throw right-click in Project window for:

• one python file
• a few selected python files
• one directory
• a few selected directories

Self-check list

Check off the item if the statement is true. Hint: [x] is a marked item.

Please do not delete the list or its items.

• I've set the proper labels for my PR (at least, for category and component).
• PR title and description are clear and intelligible.
• I've added enough comments to my code, particularly in hard-to-understand areas.
• The functionality I've repaired, changed or added is covered with automated tests.
• Manual tests have been provided optionally.
• The documentation for the functionality I've been working on is up-to-date.