Allow editing of tags in editor mode

[mliebelt]

When recording a game by using the edit mode, it would be nice to have a possibility to record the tags necessary as well:

• Provide a (simple) UI to select a tag from a list.
• Allow selection of a value (if possible).
• Allow entering of values with minimal validation (dates, integer, special values, ...).
• Use entered values as tags in the output of the printPgn command in the UI.