Raise an error if saved credentials do not have a known 'kind' (#300)
Raise an error if saved credentials do not have a known 'kind' (#300)

This fixes a problem with logging in to scalabrad-web v2 in a browser window that had previously been logged in to v1, since credentials were previously stored without a 'kind' property. These old credentials will now be rejected, so that the user will have to log in again when connecting to v2, but will at least be presented with a login box instead of a blank screen.

Fixes #299
Review: da39a3ee5e6b4b0d3255bfef95601890afd80709@pklimov 
labrad/scalabrad-web,labrad/scalabrad-web,labrad/scalabrad-web,labrad/scalabrad-web,labrad/scalabrad-web