Vocabulary as options: use the term ID

Currently when a vocabulary is used as a component option, the value that is saved in the database is the selected term name.

But this is not a correct way, because it cannot work neither on multilingual sites (@see Entity Translation and Title modules), nor when the term name is modified (which is a very basic requirement).

So it is necessary to rethink the way the options are handled. I suggest the following behaviour:

• allow either text options (multiple lines) OR vocabulary, but not both in the same time
• save the term ID when the option is "vocabulary"
• update the field formatter to get the correct term name from its ID