config: support list-type data for `probe_spec` and `detector_spec` in json and yaml configs

[leondz]

Currently only a single string of plugins & classes, separated by commas, is supported. Enable native types in config markup

Current:

JSON:

"probe_spec": "suffix,phrasing.PastTense"

YAML:

probe_spec: suffix,phrasing.PastTense

Target to also support:

JSON:

"probe_spec": [
  "suffix", 
  "phrasing.PastTense"
]

YAML:

probe_spec: 
  - suffix
  - phrasing.PastTense