Merge pull request #199 from JohnCremona/ec_url

removed hard-coded urls from elliptic curve templates
work in progress on ec_url
the wrong url in the search form gets corrected
Elliptic curve URL improvements:

  - search by Weierstrass equation now works again
  - lots of cosmetic changes in error-handling and reporting
  -  test suite updated
Merge branch 'ec_url' of github.com:JohnCremona/lmfdb into ec_url