Fix test framework loading from settings file

[tamarinvs19]

Description

Changed loading of the test framework settings from config file:

1. We parse text representation of the saved test framework
2. If it is not for java (Junit5, Junit4, Testng) we interpret as UnknownTestFramework
3. Then in Python and in Java UI logic we transform UnknownTestFramework to real test framework throw JavaTestFrameworkMapper or PythonTestFrameworkMapper

Fixes #1563

How to test

Manual tests

See #1563 and:

1. Open java project in IntelliJ IDEA
2. Check that test framework in UTBot UI is Junit4/5/Testng
3. Switch off experimental languages in UTBot settings
4. Close IDE and reopen python project and switch on experimental languages support
5. Try to generate tests with pytest (expected: tests have been created)
6. Close IDE and reopen python project
7. Check that experimental languages is active and default test framework is pytest
8. Close IDE again and reopen java project
9. Check that experimental language is active and there are no problems with java test framework

Self-check list

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• PR title and description are clear and intelligible.
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• 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.