Import documents - prevent double quoting

[PrimozGodec]

Issue

Since now Orange's UrlReader encodes special characters in URL biolab/orange3#5412, special characters are getting encoded two times in import document which makes escape characters encoded and so it produces the wrong URL.

Because of changes also self.path is quoted and so matching with metadata fails.

Description of changes

• Since it is still required to keep encoding in import documents' reader to support older versions of Orange, I propose to decode and encode URLs again. If URL is not encoded, decode does not change the URL.
• Fix matching with metadata with storing non-encoded path

Includes

• Code changes
• Tests
• Documentation

[codecov-commenter]

Codecov Report

Merging #661 (8207f30) into master (0feb2e9) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 8207f30 differs from pull request most recent head f49d85d. Consider uploading reports for the commit f49d85d to get more accurate results

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  Misses       2144     2144           
  Partials      236      236           

[PrimozGodec]

I added tests with is raised when a minimal version of orange will be set to 3.29.1