Add additional data to translation files for validation

Background / User story

See trac#104.

What to change

• Design: N/A
• Research: N/A
• Spec: N/A
• Development:
  • Add isOptional boolean property. (not necessary)
  • Add maxLength integer property.
  • Add spec string array property.
  • Add checks to translation file validation
    • Is file UTF-8 encoded?
    • Is translated string identical to source string? (ignore for strings marked with isOptional or for en-* locales) (not advised due to Crowdin contributors readding removed strings)
    • Does translated string exceed maximum length specified by maxLength?
  • Clean up custom properties when using translation files outside of UI repository
    • Remove custom properties when building or uploading to Crowdin.
    • If spec exists, serialize array and append to description when uploading to Crowdin.
    • If maxLength exists, append "Note: This cannot be longer than N characters" to description when uploading to Crowdin.
    • If feasible, pass maxLength to Crowdin so that it can enforce the length restriction on its side as well.

Hints for testers

TBD

Hints for translators

TBD

Integration notes

TBD