Fix code-style and documentation
Remove unnecessary properties and its getters/setters

refs #5525
Re-add getResourcesByType as simplified version

refs #5525
Revert backslash removal in front of namespace-less use statement
Merge EditBackendForm with CreateBackendForm and rename it

It is not necessary to distinct between whether a backend is created or
edited as a user perhaps likes to change the name of a backend directly
instead of the need to remove and recreate it.

refs #5525
Adjust editbackend-action to suit the new backend-form interface

refs #5525