optimize structure

[flo-schu]

I do a lot of double bookkeeping which is very stupid.

when I modify a Tag i also have to modify the database. Since I want to keep the database as pandas (csv) format for easy export import and compüatibility

Tag values should always only be derived from the database and not the other way round.

• creating a Tag adds one line to the database
• modification of a tag updates the respective entry in the database
• a call to the tag fetches the appropriate entries (label, ... ) or derived entries (contours, etc)

[flo-schu]

I would say this is mostly done for now. Tag has been radically reduced and most of the work relies now on the tag dataframe