Moved the implementation of exportTo* from GridFunction to the global level.
Removed an unused private method orderIncrement().
Added tests of the automatic choice of quadrature orders.
Changed the signature of TestKernelTrialIntegral::
evaluateWithNontensorQuadratureRule(), making most arguments non-constant.

This is to allow implementations modify arrays in-place, since their
contents are not used any more (in the current usage scheme).

This decision might still be reversed in future, depending on profiling
results.
Added include guards in an *_imp.hpp file.
Added the first implementation of a BLAS-based integral class.

Currently only non-tensor quadrature is done with BLAS. The code is very
"dirty" -- lots of commented out experimental code -- it will be cleaned
up later.
Selected operators can now use the BLAS-based assembler.
Added a type_combinations.hpp file for testing all relevant template
instantiations.
Added unit tests of BLAS-based assembly.
Corrected a typo in comment.
Added a code (for debugging) showing how many integrals an integrator calculated.
Accelerated DefaultLocalAssemblerForIntegralOperatorsOnSurfaces::
elementDistanceSquared().
Distance between two clusters is now estimated more accurately
(but less efficiently).

I'm not sure whether this will stay.
Cleaned up part of the obsolete comments from
DefaultTestSingleScalarKernelTrialIntegral.
Enabled BLAS-based integration in modified Helmholtz SLP.
Geometrical data are again taken as constant in evaluateWithNontensorQuadratureRule().
Added some asserts to DefaultTestKernelTrialIntegral.
Minor cleanup of the BLAS integral implementation (non-tensor case).
First (buggy) BLAS-based implementation of evaluateWithTenorQuadratureRule().

Doesn't work yet because arrays end up being modified multiple times.
Corrected the implementation of BLAS integral calc. for tensor products.