Fix to demographics.py for case of no token prompt

[jdebacker]

This PR fixes an issue with the recently updated demographics.py. When working with the module directly, users were prompted for a token. But when this function is called through other packages, this prompt doesn't seem to always appear. In case that happens, a try and except statement has been added so that even if the input prompt is not given, you the demographics still runs, resorting the the Population-Data repo.

In addition, a new utility is added that allows users to dump all the parameters from an instance of the Specifications class object into a JSON string. Among other uses, this makes it easy to create JSON files for the default parameters of different calibrations of OG-Core.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 71.93%. Comparing base (4e6ae04) to head (7255bbe).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #938      +/-   ##
==========================================
+ Coverage   71.92%   71.93%   +0.01%     
==========================================
  Files          19       19              
  Lines        4716     4725       +9     
==========================================
+ Hits         3392     3399       +7     
- Misses       1324     1326       +2     

Flag	Coverage Δ
unittests	71.93% <83.33%> (+0.01%)	⬆️

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Files	Coverage Δ
ogcore/__init__.py	100.00% <100.00%> (ø)
ogcore/parameters.py	84.30% <100.00%> (ø)
ogcore/utils.py	86.49% <93.33%> (-0.05%)	⬇️
ogcore/demographics.py	56.97% <50.00%> (+0.08%)	⬆️

[rickecon]

@jdebacker. Awesome.