Introduced sparse_matrix type, replacing ublas::compressed_matrix.

As ublas::compressed_matrix has terrible performance in debug mode,
and is the only dependency on Boost, this commit removes all
ublas-stuff and thus removes the Boost-dependency.
Note that NaN-problems for poisson_3d have not been fixed yet,
as they are inherited from an earlier commit.
Solvers: Removed spurious debug output.
Poisson 3d: Fixed missing initialization of permittivity quantity.

div(eps*grad(u)) resulted in NaNs all over the place because
eps was default-initialized to zero.
Merge branch 'karlrupp/purge-ublas' into next

* karlrupp/purge-ublas: Gets rid of uBLAS and the Boost dependency.
Introduces a custom sparse_matrix type, which is essentially nothing
but a wrapper around std::vector<std::map<IndexT, NumericT> >.
ublas::vector is replaced by std::vector.