[WFCORE-158] Don't allow handlers to be removed if assigned to a logger or another handler.
[WFCORE-159] Don't allow handlers of the same name to be added.
Merge pull request #234 from jamezp/WFCORE-158

[WFCORE-158] Don't allow handlers to be removed if assigned to a logger or another handler.
Merge pull request #235 from jamezp/WFCORE-159

[WFCORE-159] Don't allow handlers of the same name to be added.