add burnin button, and others

A few updates:

• Add a "BURNIN" button, with the load current and burnin time as the input parameter.
• Deal with annoying expired db login situation: now saves the itk db passwords per session, and when db login is expired, re-authenticate from the saved passwords
• Update the default parameters of a few functions: panel stage transition, powerboard temperature monitoring, chiller thermal cycle.

In order to make this merge request work, one needs to merge this merge request in powertools first: berkeleylab/labremote-apps/powertools!147 (merged)