REF: Refactor bias handling

[asoplata]

Re-organize External Bias handling to resemble how External Drives are handled:

• Distinguish between type and name for biases (similar to drives)
  • (This should allow for better organization of multiple biases of the same type but different names in params usage)
• Separate bias code from drive code (such as in drives.py:_add_drives_from_params())
• Update config file format to reflect these changes, including both separation of type and name
  • Note that for this reason, this should probably be done after MAINT: Upgrade ALL network configuration file formats (except for tests) #962 is complete.
• Un-hardcode any current code that only uses tonic (such as params.py::_extract_bias_specs_from_hnn_params())
• What else?

[jasmainak]

Don't think any "refactor" issue is a "good first issue" ;-) Do keep in mind that if you change the internals in a way that it may break user code, you would have to deprecate ... if it's just moving private functions around, then there is no need to worry of course.

particularly if you want the code to be adopted outside Jones lab; it is sometimes better to keep sub-optimal code if it doesn't break old user code.