📦 Add all/filtered/selected CSV export actions

[AndyScherzinger]

Closes #1412 #1436

• Implements contextual CSV export with three options:
  1. all
  2. filtered
  3. selected
• Now, in addition when a filter is active (via the header-filtering) is present another menu item is shown in both menus
• Since exports are always CSV I dropped that technical term (can be added again of course)

🏚️ Export (header)	🏡 Export (header new)	🏡 Export (header filter new)	🏚️ Export (selection)	🏡 Export (selection new)	🏡 Export (selection filter (new))

[AndyScherzinger]

@marcoambrosini @jancborchardt for designer feedback regarding the menus, their item text and the dynamic adding/location of the new item(s). I started with a first, best-guess. Anything can be changed of course but wanted to start somewhere. It is purely front-end because the back-end has already been capable and I also have been confused with the generec items in the past on assuming what will get exported. So this makes any of the 3 options very explicit in what to expect if you hit the export item.