Register Windows file associations properly

Fix two defects:
1. Use proper ProgID in the form Poedit.*
2. Don't uninstall extension registry key

See http://msdn.microsoft.com/en-us/library/windows/desktop/hh127451(v=vs.85).aspx
More compact Finder/Explorer filetype kind strings

Don't say "PO Translation File", say just "PO Translation" - that "file"
is redundant and native apps tend not to use it.
Windows: Localize Explorer file kind strings
Update lproj handling in Crowdin script

Fix after changed location.
Fix copyright string in InnoSetup script
Fix wrong support email in InnoSetup script
Use InnoSetup translations

Only enable the officially maintained InnoSetup translations, don't
integrate with Crowdin or use custom translations for other languages -
it's not worth the hassle for just an installer.
Fix crash when updating from sources w/ sidebar on

Fixes #121.
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.
Use HTTPS for updates checking
Fix makefiles broken by i1n scripts changes

Fix breakage introduced in 9586e7fb.