[product.l2] major refactor
* all traits are now in namespace internal
* added all variants of WeightedL2
* derived L2 from WeightedL2
* added over_integrate option
[tests.operator_products] update
[product.ESV2007] removed obsolete WeightedL2
[tests.elliptic-swipdg...] updated products
[product.elliptic]
[tests.elliptic-swipdg...] add estimator and efficiency
[tests.elliptic-estimators] report on all errors