[REQUEST] add custom columns

[TheElo]

Is your feature request related to a problem? Please describe.
I would like to have a feature to add custom columns

• you have a couple of rating services, but do not allow the user to have a own rating column
• some games, just need a small comment here and there
• or information for personal state like "active, won't play" and so on
• tags, come one we all know steams tags are sh#t

Describe the solution you'd like
In the database editor, add a button to add a custom column and let the user name it and set data type
by double clicking in the viewer the user can directly type into the cell or gets a prompt box

Describe alternatives you've considered
Alternatively I looked into managing that in excel, but it's rather hard to link to json files there (a export function to a csv would be helpful too)