[FIX] ExcelReader - Use openpyxl to read xlsx and xlrd for xls

[PrimozGodec]

Issue

• Tests started to fail since xlrd cannot read xlsx files on newer Pythons. It is also documented in the library that it supports only historic xls files. While writing tests for the historical version of xls, I noticed that the version of xlrd pinned in requirements doesn't work with Pandas anymore, so data cannot be loaded from xls.
• With the newest scipy (1.12.0) mtx loading started to fail since they implemented the module.

Description of changes

• Use Openpyxl to get info on xlsx and xlrd for gen info for xls. Adding openpyxl to requirements. It is already an Orange3 requirement. Updating the version of xlrd to work with Pandas
• It seems that mtx file opened as "rb" failed. Instead of opening it manually, pass the filename to the module, and it will open itself.

Includes

• Code changes
• Tests
• Documentation

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.59%. Comparing base (40341cd) to head (68edf7a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #400      +/-   ##
==========================================
+ Coverage   80.56%   80.59%   +0.03%     
==========================================
  Files          21       21              
  Lines        5474     5479       +5     
==========================================
+ Hits         4410     4416       +6     
+ Misses       1064     1063       -1     

Files	Coverage Δ
orangecontrib/single_cell/widgets/load_data.py	93.12% <100.00%> (+0.24%)	⬆️

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