Smart tagging of merged trips

I noticed, that when merging two trips when one or both of them have tags already assigned those tags get lost on the merged trip. Furthermore auto-tagging based on start/destination (means: Tagging based on older tags for same route) is not applied after merge.

I suggest to handle this in a more smart way as follows:
1. The merged trip should contain all tags previously assigned to the single trips
2. Automatically trigger the auto-tagging again after the merge process

Especially no. 2 would be helpful if you drove the usual route, which is already known to Tronity but stopped in between. Right now you get two untagged trips and also after merging it wont get automatically tagged.