Added SPE10 header and data files
Added function "hasExactSolution" to problem (defaults to false!)
Rearranged loops in coarse matrix assembler to speed up
Reindented matrix assembler (ONLY WHITESPACE CHANGES!)
Added SPE10 to buildfiles
Added first source term to SPE10 problem
introduced hasExactSolution everywhere
Disabled incompatible non-used ImprovedL2Error class

Please check, whether anyone still uses this, 
we should remove it eventually.
Fixed warning about struct being previously declared as class
Bugfix: Variable defined multiply