Add edit state information to courses.

This commit introduces two new optional values for phrases:

i18nText:
the English text string that is defined in the course skeleton (if
present); this string will be used to notice changes in the skeleton
phrase wordings and possibly can used in the future for localization

editState:
this state reports whether the state of a phrase is "unknown",
the string is at least "translated" or if it is "completed" (including
phoneme tagging and recording)

These information can be omitted when distributing courses.