VCS[CVS]: Complement menu options, support 'edit'.
Add missing menu options for project/repository actions. Add support for 'edit' (current file) and 'unedit' (current file/repository, with prompt). Note: Unediting modified files will only work with cvsnt, since it uses the '-y' option to force a 'yes' to CVS asking to revert changes. Implement IVersionControl::vcsOpen() by using 'edit', causing it to prompt for read-only as it does for Perforce. Task-number: QTCREATORBUG-1971 Task-number: QTCREATORBUG-1864