Allow twgit to send an email on hotfix and release finish

[Sebastien-Hanicotte]

An idea from @aluput was to configure and send an email when closing a release / hotfix.

This email would list all the features merged in the release and display all comments for every commits in those feature.

I let this feature to discussion, but it will certainly based on a user/project specific configuration like the use of a .twgit with new options.

[geoffroy-aubry]

Same idea from an another team today :-)
When opening, closing, removing a release or hotfix.