Thermal+storage (fusion, maintenance)

[cfe316]

This is a draft pull request, just to show everyone what might should be coming down the pipeline soon. The branch is currently based on v0.3.6, not on develop, so that why I've done it this way for now.

I am pretty happy with how I wrote up the formulation thermal_storage.jl. There are some new techniques here.
I'm also happy with the more simplified output files as seen in write_thermal_storage.jl.

TBD:

• A serious capacity_reserve_margin+storage formulation.
• Maybe change maintenance to act on the generator rather than the thermal core?
• Or perhaps even allow a separate formulation for each? (they'll have to sync up, optimally!)
• Documentation
• Existing capacities and retirements, not just new-build.

[codecov-commenter]

Codecov Report

Merging #546 (8ad206a) into develop (951179b) will increase coverage by 0.18%.
Report is 34 commits behind head on develop.
The diff coverage is 0.00%.

❗ Current head 8ad206a differs from pull request most recent head 48ca683. Consider uploading reports for the commit 48ca683 to get more accurate results

@@            Coverage Diff             @@
##           develop    #546      +/-   ##
==========================================
+ Coverage     0.07%   0.26%   +0.18%     
==========================================
  Files          112     115       +3     
  Lines         3800    4562     +762     
==========================================
+ Hits             3      12       +9     
- Misses        3797    4550     +753     

Files	Coverage Δ
src/configure_settings/configure_settings.jl	0.00% <ø> (ø)
src/write_outputs/write_costs.jl	0.00% <0.00%> (ø)
src/write_outputs/write_emissions.jl	0.00% <0.00%> (ø)
src/load_inputs/load_fuels_data.jl	0.00% <0.00%> (ø)
src/model/generate_model.jl	0.00% <0.00%> (ø)
src/write_outputs/write_net_revenue.jl	0.00% <0.00%> (ø)
src/write_outputs/write_outputs.jl	0.00% <0.00%> (ø)
src/model/resources/thermal_storage/maintenance.jl	0.00% <0.00%> (ø)
src/load_inputs/load_generators_data.jl	0.00% <0.00%> (ø)
src/write_outputs/write_thermal_storage.jl	0.00% <0.00%> (ø)
... and 1 more

... and 35 files with indirect coverage changes

[cfe316]

Closing because this is not ready, and will need to be substantially reworked.