Modular Abelian Varieties

Todo on March 16

Move functions out of abvar_modsym_factor into abvar and delete that file.
Torsion subgroups:
- Refactor base class
- Get implementation to work with defining data being (lattice, abvar); compute generators.
Decomposition:
- three types:
  - ungrouped as simple abvars (default)
  - groups abvars
  - over End(A)
Label function
Create from label
Create a small mock database
Compute the Hecke algebra image in End(A) and find a good clean way to represent for Hecke stable. New object that is a subring of End(A). Have methods like R.index_in(S).
Compute End(A) in general.
Morphisms:
- Kernels
- Cokernels
Quotients by finite subgroup
Intersection pairing
Poincare Reducibility:
- projection
Quotients by abelian subvariety
Minimal isogeny degree for A, B simple.