Allow to enable / disable options, instead of forcing deletion

[SamBrishes]

Add possibility to (de)activation properties / configuration model items instead of the need to delete them.

Especially for

• [x] Currencies
  • [x] Implementation
  • [x] Testing
  • [x] Exception handling (See comment below)
• [x] Price Categories
  • [x] Implementation
  • [x] Testing
• [x] Taxes
  • [x] Implementation
  • [x] Testing
  • [x] Test how taxes are selected with and without shipping country / enabled state.
• [x] Payment methods
  • [x] Implementation
  • [x] Testing
• [x] Shipping methods
  • [x] Implementation
  • [x] Testing
• [x] Order States
  • [x] Implementation
  • [x] Don't allow disabling order states when flag is assigned
  • [x] Testing

[SamBrishes]

Testing / Exception handling What happens with currencies that were still active when they were used but were deactivated afterwards?

-> Should be shown where it has been already "used", hide where it "could be used". A helping "enabled" query scope is already in the model.

[SamBrishes]