Fix lupdating being broken

[OPNA2608]

lupdateing the project was broken because the translations weren't able to access the C++ code with the translatable strings from the data subproject. It works again now. It bothers me a bit to move the translations out of /data again but I think it's cleaner than the alternatives. At least now everything in /data is purely copy-pasted into the target directory, and everything outside of it is code or otherwise transformed / integrated into the build. (resources, lang)

Ran: lupdate Project.pro

Before PR: Considers all existing translations as obsolete because it can't find any code references to them.

Updating 'data/lang/bamboo_tracker_fr.ts'...
    Found 0 source text(s) (0 new and 0 already existing)
    Kept 826 obsolete entries
Updating 'data/lang/bamboo_tracker_ja.ts'...
    Found 0 source text(s) (0 new and 0 already existing)
    Kept 826 obsolete entries
Updating 'data/lang/bamboo_tracker_pl.ts'...
    Found 0 source text(s) (0 new and 0 already existing)
    Kept 826 obsolete entries

At the end of the PR: Finds already translated & new translatable strings in code.

Updating 'BambooTracker/lang/bamboo_tracker_fr.ts'...
    Found 818 source text(s) (9 new and 809 already existing)
    Kept 17 obsolete entries
    Number heuristic provided 3 translation(s)
Updating 'BambooTracker/lang/bamboo_tracker_ja.ts'...
    Found 818 source text(s) (9 new and 809 already existing)
    Kept 17 obsolete entries
    Number heuristic provided 3 translation(s)
Updating 'BambooTracker/lang/bamboo_tracker_pl.ts'...
    Found 818 source text(s) (9 new and 809 already existing)
    Kept 17 obsolete entries
    Number heuristic provided 3 translation(s)

After PR: Still finds already translated strings in code.

Updating 'BambooTracker/lang/bamboo_tracker_fr.ts'...
    Found 818 source text(s) (0 new and 818 already existing)
Updating 'BambooTracker/lang/bamboo_tracker_ja.ts'...
    Found 818 source text(s) (0 new and 818 already existing)
Updating 'BambooTracker/lang/bamboo_tracker_pl.ts'...
    Found 818 source text(s) (0 new and 818 already existing)

[OPNA2608]

Fixed the .qm path creation on older Qt versions. Also had to move all the path variables defined in /data/data.pro to the global /qmake/variables.pri so lang.pri can access the appropriate DATA_INSTALL_PATH.

[rerrahkr]

The CI error does not seem to be related to this issue, so I will merge this PR.
Thanks for your contribution!