Updated minimum doxygen version to 1.8.7
Updated one more check
Check for 1.8.7 or newer instead of just 1.8.7
Removed sections from manual

Removing sections prevented the erroneous extra end section tag. I do not
know why, though.
Updated config to 1.8.7
Merge branch 'bug-17991-update-required-doxygen-version'

Conflicts:
	Plugins/org.mitk.gui.qt.viewnavigator/documentation/UserManual/QmitkViewNavigator.dox