Create consistent tag naming scheme

The current tag naming scheme is a total mess and requires fixing:

• create an overview of all special/mandatory tags that currently exist, indicate if a tag can have two different names
• define a naming scheme, give it a version as well
• add a prefix to tags that are special (i.e. tags that have actions connected to them)
• document naming scheme, call it a specification or something
• raise errors/warnings when tags as missing or not defined (properly)
  • tags in master but in spreadsheets
  • tags in spreadsheets but not in master
• make sure users can not be surprised by unexpected default values popping up
• make sure the DLC master spreadsheet is consistent with the new naming scheme
• figure out how to warn users when their mixing tag specs