Translation Files Cleanup

[Kenny-Hui]

This PR:

• Reformat all XLIFF documents
• Synchronize <source> text and missing entries from en-US.xlf to all files
• Rename all instance of openBVE to OpenBVE
• Rename duplicated entry id (Those within the same group that is, which makes it unidentifiable)
• • train_default, train_default_yes and train_default_no is moved to menu group, fixes empty dialog box in the GL Menu when asked whether to use the route's default train.
• • creation_header has been split to creation_header (Create a package) and enter_details_header (Enter package details)

Motivation: Transifex does not seems to be in sync anymore and no new translation appears. It also seems to untranslate duplicated units id across groups (Which is technically correct as defined by XLIFF specs), as such some string remains untranslatable. I have plan to translate zh-HK locally, but I would rather have this PR merged before working on it.

I have explored different parts of UI in various languages and it seems to show no regression so far, so I hope everything did indeed go as planned. Any further amount of testings are welcome.

(For XLF file editing, I've tested and POEdit can edit all entries regardless of its id. Alternatively I've built my own XLIFF editor which should just be good enough to work with OpenBVE translations, for now.)

[leezer3]

Thanks.

I believe the problem with Transifex is (essentially) something to do with the fact that duplicate keys are undefined in XLF format as to what should happen. This was an oversight when this was originally written, which nobody has got as far as correcting.

(Transifex is acceptable, but the syncing is now a mess. There was originally a bot which synced, but the service which this depended on got withdrawn. It's built-in sync just seems to make a mess :/ )