fix: strip dots (and other chars) in fragment id of markdown links

[davorpa]

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Description

• Hotfix over fix spaces and dots in fragment id of markdown links #7021 using same branch as continuation
• Applies suggestions made at fix spaces and dots in fragment id of markdown links #7021 (comment) to complete . stripping
• Recover changes and resolves suggestions made in Add Django and Flash playlists to free-courses-ko.md #7010 (comment)
• Strips other characters like &, /, +, #... to be compilant with Kramdown GMF processor. Regex: \(#.*?[\.&\\/\+].*?\)

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