Refactor graphs, streamline some polyhedral constructors

[lkastner]

• Reduce duplication
• Let {add,rem}_edge! return bools whether operation succeeded.
• polyhedral_fan and normal_toric_variety now use the same order of arguments as polyhedral_complex. @YueRen
• Due to Matrix{Int} being used for both encoding incidences or rays in normal_toric_variety it was impossible to cleanly deprecate all old constructors.
• Rename pm_tdivisor to pm_object as this is used everywhere else.

[lgoettgens]

• Let {add,rem}_edge! return bools whether operation succeeded.

Are there situations where this does not succeed? If yes, that would imply that I need to check the return value every time to be sure, right?

[lkastner]

• Let {add,rem}_edge! return bools whether operation succeeded.

Are there situations where this does not succeed? If yes, that would imply that I need to check the return value every time to be sure, right?

yes

[YueRen]

Ah, I see that you already changed groebner_fan for me, much appreciated!

[codecov]

Codecov Report

Merging #2952 (a621b88) into master (1f2b71b) will increase coverage by 25.34%.
Report is 4 commits behind head on master.
The diff coverage is 87.71%.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2952       +/-   ##
===========================================
+ Coverage   55.15%   80.49%   +25.34%     
===========================================
  Files         511      521       +10     
  Lines       69234    70405     +1171     
===========================================
+ Hits        38185    56676    +18491     
+ Misses      31049    13729    -17320     

Files	Coverage Δ
experimental/FTheoryTools/src/auxiliary.jl	93.50% <100.00%> (+23.80%)	⬆️
...ricVarieties/AlgebraicCycles/special_attributes.jl	100.00% <ø> (ø)
...ometry/ToricVarieties/CohomologyClasses/methods.jl	60.00% <ø> (+4.00%)	⬆️
...ies/NormalToricVarieties/standard_constructions.jl	99.24% <100.00%> (+0.75%)	⬆️
...ebraicGeometry/ToricVarieties/Proj/constructors.jl	92.72% <100.00%> (ø)
...eometry/ToricVarieties/ToricDivisors/attributes.jl	100.00% <100.00%> (ø)
...metry/ToricVarieties/ToricDivisors/constructors.jl	89.79% <100.00%> (+12.24%)	⬆️
...eometry/ToricVarieties/ToricDivisors/properties.jl	78.57% <100.00%> (ø)
...Varieties/ToricMorphisms/standard_constructions.jl	100.00% <100.00%> (ø)
src/Combinatorics/Graphs/functions.jl	93.45% <100.00%> (+4.37%)	⬆️
... and 6 more

... and 321 files with indirect coverage changes