Allow YAML file defaults (especially 'server' information and password) to be stored in ~/.qca/

[jchodera]

Is your feature request related to a problem? Please describe.
I am an idiot who has disclosed the server.password field as plaintext a dozen times.

Describe the solution you'd like
It would be convenient if I could instead keep a tidy ~/.qca/defaults.yaml file with useful defaults, like the server block for qcfractal, and then only have to worry about configuring other YAML files to not contain the defaults.

Describe alternatives you've considered
I have attempted reduce the frequency and magnitude of my idiocy, without success.

Additional context