snap_polygons FromLimsSource functionality broken

[tmchartrand]

Describe the bug
The snap_polygons module has a FromLimsSource option to pull input arguments from LIMS queries, but it refers to outdated code in argschema, failing to run at all. Some minor usability changes will also be helpful in supporting use of this functionality.

To Reproduce
Follow the example usage from the command line:

python -m neuron_morphology.snap_polygons
    --host <lims host> 
    --port <lims port> 
    --user <username> 
    --password <password> 
    --database <lims db> 
    --focal_plane_image_series_id 522408212 # for instance
    --output_json output.json

Expected behavior
Successful run of the module, producing modified polygons and other output.

Actual Behavior
ImportError: cannot import name 'ArgSource' from 'argschema.sources'
(ArgSource should be ConfigurableSource).

Environment (please complete the following information):

• OS & version: Centos 7
• Python version 3.7
• neuron_morphology version: current dev branch

Additional context
It's possible this issue is partly due to using the wrong version of argschema (versions are not specified by tags for that repo), but it occurs for both a pip install from neuron_morphology requirements, and installation from source from commits that seem to be on the correct branch (input_source_3.0a). There are some related mixups in the argschema docs, see AllenInstitute/argschema#106.

Do you want to work on this issue?
Yes, will submit PR shortly

[wbwakeman]

includes #189