Respect group members in mentionable concern
Improve commit diff

* show highlights when replace empty line with content
* show inline diff when replace line with spaces with content
Fix several_namespaces? to work with multiple ownership of groups
Version 6.0.2

Includes next fixes:
* Respect group members in mentionable concern - 626359831402aeede4c4cb12cb10c7534a0dae79
* Improve commit diff - 9109a207589c3a3d085005ee87049bba6aeecc1a
* User cannot select namespace for new project - e19526c2ac3e6a8ae62934c09ac70219062c818a