Upgrade to frigga-0.9 in order to be able to parse image appversion tags where the version number contains letters.
Refactored to use self-explanatory named constants instead of magic number.
Refactored to avoid parsing text into JSON only to turn the JSON back into text on the same line.

This way we just take the text as a string more simply.
Merge pull request #552 from joesondow/Upgrade-frigga-for-letters-in-version

Upgrade frigga for letters in version, and minor refactoring