[ENH] Use ISO language setting in widgets

[PrimozGodec]

Issue

In the beginning, I was keeping language names in widget settings. It turned out it is better to keep languages as ISO codes since language names can change in the future (like we did with Ancient Greek), but ISO codes will probably not.

This

Description of changes

• It should fix the issue reported in https://github.com/biolab/orange3-text/pull/1030
• Change the Ancient greek language to Ancient Greek to be compatible with other languages (and compatible with ISO standards).
• Keep languages as ISO codes in settings to bypass problems with language name changes and easier management.

Includes

• [X] Code changes
• [X] Tests
• [ ] Documentation

[codecov-commenter]

Codecov Report

Merging #1034 (c6a7082) into master (e7c360d) will increase coverage by 0.23%. The diff coverage is 92.10%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1034 +/- ## ========================================== + Coverage 82.18% 82.42% +0.23% ========================================== Files 92 92 Lines 12283 12322 +39 Branches 1670 1678 +8 ========================================== + Hits 10095 10156 +61 + Misses 1880 1855 -25 - Partials 308 311 +3 ```