Show only own tags in the auto-completion dialog

[tanius]

When creating an annotation and entering a tag for it, the auto-completion field will list fitting tags authored by any user. However, only tags from the same user should be shown. Else, the tag auto-complete namespace is cluttered with non-relevant proposals, and a user does not have the option to name a tag the same as another user did.

To implement this, an author field should be added to the openethnographer taxonomy.

Only showing own tags does not hinder collaboration, as users will be able to fork others' tags to re-use them. The forked tag is their own and its name will appear in the auto-complete dialog.