Tags migration only installs 1/6

[rosiel]

The tags migration will run but only install the first tag. No amount of rolling back/update will get it to install more than the first value.

I think it's due to the Migrate Source CSV plugin now installing the 3.x branch, which changed the syntax. Instead of keys we now specify a uniquely identifying column under the id parameter. This seems to default to the first column, vid, which of course is the same for all tags so only one gets migrated.

PR to come.

[jordandukart]

Merged in the above, thanks @rosiel!