Leverage MT merge for project versions

I would like to use MT as another source of translations to copy from when performing TM merge or copy trans. I should be able to tell the source of the translations when looking at its history.

Todo:

• filter of MT translation (GWT)

• restrict to certain permission/role

• The new modal for MT merge in version level (all languages or single language)

• option to override fuzzy or not

• option to save as translated or fuzzy

• schema change to textflowtarget for MT + engine

• fix 1 MT engine from Zanata

• MT credential in system properties

• MT translation should be excluded from TM suggestion

• Any modification will clear the MT flag

• Include attribution into the translated file and UI in Zanata

• MT option only available to pot/po, properties and xml file format as part of legal attribution requirement from the backend engine, e.g. Google

UX: https://github.com/zanata/zanata-platform/pull/919