Plainly

This merge requests changes the typing, subtyping, environment splitting and environment copying judgments to be Plain, by wrapping them in a plainly modality. Furthermore, it fixes the proofs the typing rules for copy- and adds some missing rules.

This is based on the copying branch, hence that branch should probably be merged first.

added 2 commits

• 76e4661d - 1 commit from branch master
• 7b1bbf2b - Add plainly, fix copy- rules

Compare with previous version

mentioned in commit 12aa1f34

merged