[operators.ei] add EmpiricalInterpolatedOperator
[algorithms] add ei algorithms
[demos] add burgers_ei demo
[operators.constructions] bugfix
adapt ei code to new VectorArrayInterface
Merge branch 'master' into burgers_ei
get burgers_ei demo running again
[algorithms.ei] add support for orthogonal projection during basis generation
[algorithms.ei] rename generate_interpolation_data -> generate_ei_data
[la.numpyvectorarray] bugfix
[demos.burgers_ei] use original discretization for greedy

instead of ei_discretization.
[algorithms.ei] cleanup
[operators.ei] cleanup
[algorithms.ei] add dofs and collateral basis to 'data' return value
[operators.fv] bugfix
[grids.boundaryinfos.SubGridBoundaryInfo] bugfix
[demos] enhance burgers_ei demo
Merge branch 'burgers_ei'