increase version moccml engine plugins

Similarly to what we've done with other GEMOC components, we should increase the version number used by moccml plugins in order to reflect that it is now part of Gemoc at eclipse and not anymore part of the older project.

So I suggest moving from 2.3.0 to 3.0.0 (as a major change) and then continue to increase the version numbers depending on the content that has changed between releases (changes are tracked repository per repository using (gren)[https://github.com/github-tools/github-release-notes] in order to populate the changelog from the pull requests see https://github.com/eclipse/gemoc-studio/wiki/Official-commiter-memo)