Append, but not override tags in exif

[akawana]

Hello,

We started to use your wonderful application all around the team artists. Our image collections are shared (through google drive, microsoft onedrive and our own SVN repository).

The problem appear when people add tags before updating (importing) them from the images. I suggest not just override all the tags, but try to append the new and check if other already exist.

This can be optional. Even if separator standard (| \ / :) is different between two people it is possible to compare, add and then covert to the current client standard.

I think this problem is related with auto export and auto import issue mentioned here before.

Thank you.