Calculate shape functions using FEMBasis.jl

A lot of code is moved to FEMBasis.jl regarding
calculating basis / shape functions of finite elements.

* add FEMBasis to REQUIRE
* remove obsolete files
* remove obsolete test files
* make integration point iterable
* loosen type definitions
* get length of element rather from basis than connectivity
* calculate midpoint of reference element
* wrong input argument to eval_basis! fixed

src/problems_dirichlet.jl

@@ -56,7 +56,7 @@ function assemble!(problem::Problem{Dirichlet}, time::Float64=0.0;
             for i=1:field_dim
                 haskey(element, field_name*" $i") || continue
                 ldofs = gdofs[i:field_dim:end]
-                xis = get_reference_coordinates(typeof(element.properties))
+                xis = get_reference_coordinates(element)
                 vals = Float64[]
                 for xi in xis
                     g = element(field_name*" $i", xi, time)