Restructure toric varieties with a view towards toric blowups to come.

[HechtiDerLachs]

CC: @HereAround

[codecov]

Codecov Report

Merging #2795 (165bfac) into master (3df9a13) will increase coverage by 0.05%.
The diff coverage is 56.66%.

@@            Coverage Diff             @@
##           master    #2795      +/-   ##
==========================================
+ Coverage   73.54%   73.59%   +0.05%     
==========================================
  Files         455      456       +1     
  Lines       64445    64445              
==========================================
+ Hits        47396    47429      +33     
+ Misses      17049    17016      -33     

Files Changed	Coverage
src/AlgebraicGeometry/ToricVarieties/JToric.jl	ø
...ies/NormalToricVarieties/standard_constructions.jl	ø
...aicGeometry/ToricVarieties/Blowups/constructors.jl	56.66%

[fingolfin]

According to @HereAround it would be nice if first PR #2780 gets ready and merged and then this one here, so I am not expecting changes here for now...

Next week @HereAround and @HechtiDerLachs and maybe others will discuss this and come up with a plan on how to proceed.

[HereAround]

I believe I addressed this and more in my changes to #2780. Unless you object @HechtiDerLachs , I will close this PR.