ST6RI-738 Syntax-related issues from KerML FTF Ballot #5

[seidewitz]

This PR implements resolutions of issues from KerML FTF Ballot 5 that called for updates to the KerML abstract and concrete syntax.

Resolutions of the following issues are implemented in this PR:

• KERML-82 checkConnectorTypeFeaturing is not correct
• KERML-98 Comment Locale not in textual notation
• KERML-165 Exponentiation should be right-associative
• KERML-307 User-defined keywords are not allowed on metadata features

Resolution of the following issue only affected the generated UML metamodel files included in PR #534:

• KERML-22 Name all associations in the KerML abstract syntax

[himi]

I could even evaluate KERML165:

[himi]

I'll review ST6RI-740, for SysML, hopefully tomorrow.