[FIX] Replace pdfminer3k with pypdf

[PrimozGodec]

Issue

Fixes https://github.com/biolab/orange3-text/issues/964

Description of changes

pdfminer3k is not maintained for a few years now. In this PR, I am replacing it with pypdf, which looks maintained and is a pure Python package.

Includes

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

[codecov-commenter]

Codecov Report

Merging #994 (1cb5734) into master (96a9548) will decrease coverage by 0.14%. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #994 +/- ## ========================================== - Coverage 82.20% 82.06% -0.14% ========================================== Files 93 93 Lines 12284 12264 -20 Branches 1664 1661 -3 ========================================== - Hits 10098 10065 -33 - Misses 1874 1889 +15 + Partials 312 310 -2 ```

[PrimozGodec]

/rebase

[PrimozGodec]

/rebase