Add titles to all the _index files in the directories
Merge branch '20' into 21

Conflicts:
	Database-Model/_index.md
Fix sidebar generation
Merge branch '21' into 22

Conflicts:
	Commercial-Features/Commercial-Payment-Modules/_index.md
	Commercial-Features/_index.md
	Database-Model/Modules-Model/_sidebar.md
	Database-Model/_index.md