Remove obsolete login check
After sign-in, close info messages on SignInScreen

This fixes #32 in csdms/wmt-client.
Implement "tag/model/remove" from API

Allows a label to be detached from a model. The label isn't deleted --
it can be reattached with the "tag/model/add" API call.
Merge pull request #39 from mdpiper/master

Implement the new "tag/model/remove" APL call