Feature request: Allow import/export (+sharing) of groups

[johschmitz]

First of all this is a low priority feature request since I don't believe that many people would really use it but I guess it might useful for some few out there.
You could allow import/export and sharing of a group like this:

1. Export group as a json string from the database
2. Compress json
3. Encode to Base64
4. Base64 string can just be shared in a message
   For import go backwards.

Possibly merge the imported group with an existing group such that two people can collect expenses in a distributed way and merge at the end of the day. With that last possibility the whole feature might become quite useful. So during import ask the user with which existing group he would like to merge the imported data.