entry table: offer a tiny context menu for adding/removing columns

[ilippert]

Is your suggestion for improvement related to a problem? Please describe.
I'm always frustrated when I want to change the entry columns. I have to click at least 3 times to get to the respective setting.

Describe the solution you'd like
I would love to be able to use right click onto the column headings and then get a context menu that allows me to activiate/deactive default or manually configured columns; ideally I would also be able to change the order of columns.

Additional context
This seems to be a quite widespread way of changing table columns, thinking of spreadsheets or file browsers, email clients.

[ilippert]

closing in favour of #6601