[FIX] Removed warnings filters, DeprecationWarnings replaced with FutureWarning

[PrimozGodec]

Issue

• Warning filters override filters from other packages (e.g. filter for OrangeDeprecationWarning was overridden - test started to fail)
• DeprecationWarning can be replaced with FutureWarning:

  Base category for warnings about deprecated features when those warnings are intended for 
  end-users of applications that are written in Python.

  As far I understand DeprecationWarning is made for developers of the package (in your case openTSNE developers), while FutreWarning is for users of your package. FutreWarning is printed by default.

Description of changes

• Removed filters
• DeprecationWarning replaced with FutureWarning

Includes

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