Ordering the elements in the output

[pogudingleb]

Functions for assessing identifiability now return OrderedDict in which the ordering is

• if funcs_to_check argument was passed, then the ordering is the same as in funcs_to_check
• otherwise first the states are listed (in the same order as in the system) and then parameters.

This PR addresses #244

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2ff1a9d) 65.70% compared to head (f0a111d) 88.00%.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #247       +/-   ##
===========================================
+ Coverage   65.70%   88.00%   +22.29%     
===========================================
  Files          25       25               
  Lines        3184     3192        +8     
===========================================
+ Hits         2092     2809      +717     
+ Misses       1092      383      -709     

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