Refactor FEAT report generation

[brandynlucca]

This PR includes:

• New function [distribute_transect_estimates] that performs a similar operation as distribute_kriged_estimates.
• New class [FEATReports] that incorporates a variety of helper functions and methods to produce each report-type
• Tests and fixtures for all helper functions, FEATReports initialization, and methods
• Minor bug fixes

[leewujung]

@brandynlucca : Thanks for the PR. I have an inline comments about merging distribute_krige_estimates and distribute_transect_estimates, and some other comments below:

Could you add a notebook to show the exact steps to generate report using the class? I am not able to find it. I added an issue to track that. #397

test_FEATReports sits in test_class.py which only has 1 test underneath. Would be better to just change that to test_FEATReports.py. Are there other classes you plan to test in this script?

[brandynlucca]

• The distribution functions have been consolidated to a single distribute_population_estimates()
• report_generation.py workflow example/demo file now exemplifies FEATReports usage

This can therefore be merged.