Remove DRalgo and factor code to only contain model generation from DRalgo

[pschicho]

this is based on PR #5 but immediately gets rid of DRalgo stuff.
Fixes:

-Fixed typos and bugs
-Added generation of full matrix-elements, even those strictly beyond leading log
-Particle masses are included in all propagators, including s-channel ones
-Added export/import to json
-More compact expressions for all scattering channels
-Removed an overall factor of 1/2 -->Make sure to add this in the *.cpp files
-Added support for scalar particles
-Added t<->u flips to preserve crossing symmetry
-Added crossing-symmetry relations in order to use less channels
-Added full SM example file together with the results in an accompanying .json file.
-Added generation of matrixelements via Feyncalc (+generation of the model files with Feynrules)

• double loading of DRalgo since the code is now standalone
• s,t,u conventions in .txt files
• warnings for multiple light species
• light particle listed in JSON files
• truncation at LL

--------------------------To add to this PR--------------------
-More test files
-Could be good to add more Feyncal examples while we are at it
-Updated examples with the new syntax

[og113]

I had a few comments and questions, but this is a major improvement on main. Great work.

[pschicho]

Sorry, I'm just trying to understand the changes to the code, which look pretty large. The source code is now split into 3 files:

• matrixElements.m - this was the only file previously
• modelCreation.m - this looks like it was taken from DRalgo
• WallGoMatrix.m - how does this file relate to what was there before? does it contain some subset of what was in matrixElements.m before? Or mostly new stuff?

The original matrixElements.m is now split into the new matrixElements.m and WallGoMatrix.m. The only module necessary from DRalgo was modelCreation.m.

[og113]

I think everything crucial has been done now, so we are ready to merge to main (and then make the repo public).