Improve translation management scripts

Do a few changes to make maintaning the PO files simpler:

1. Move all scripts into scripts/
2. Remove source code location information from PO(T) files. It's mostly
   useless and produces noisy diffs with lots of unimportant changes.
3. Upon updating from Crowdin, refresh POT and POs to get consistent
   formatting and up-to-date strings.
Regenerate poedit.pot and PO files
InnoSetup: don't ask for inst dir when upgrading
Remove the old HKCR\GettextFile file association

Leaving the registry key in would confuse Explorer, which would think
there are two apps registered and would ask the user which one to use.

Clean after older Poedit versions.
InnoSetup: delete old version's ICU files

After updating ICU, the filenames changed from using "52" in the version
to "54". These files are large, make sure there are no leftovers after
Poedit 1.6.
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