QR: add isInjective(), isSurjective(),

mark isFullRank() deprecated,
    add solve() (mix of Keir's patch and LU::solve())
=> there is big problem with complex which are not working

test/sparse_basic.cpp

@@ -193,7 +193,6 @@ template<typename SparseMatrixType> void sparse_basic(const SparseMatrixType& re
         }
       }
       m2.endFill();
-      //std::cerr << m1 << "\n\n" << m2 << "\n";
       VERIFY_IS_APPROX(m2,m1);
     }