refactored elliptic curve isogeny classes to use their own class
new encode_plot function in utils
Use stored isogeny matrices instead of recomputing on the fly
Part 3 of elliptic curve refactoring: WebEC class
tidying up elliptic curve isogeny class page
Merge pull request #193 from JohnCremona/ec-refactor

Ec refactor
Merge branch 'master' of https://github.com/LMFDB/lmfdb