Support accessing eigen_matrix elements in eigen_typekit

[xwavex]

I would like to use the [ , ]-operator for eigen_matrix to get and set elements.
I saw that there is already an attempt in the code to achieve that, but unfortunately, newTernaryOperator seems to be missing.

So I tried to get the input for a statement like this mat[0,1] by utilizing the getMember function for the MatrixTypeInfo.
Using the following cast, I am able to get the first index in this case 0, but not the second one.

RTT::internal::DataSource<int>::shared_ptr id_indx = RTT::internal::DataSource<int>::narrow( RTT::internal::DataSourceTypeInfo<int>::getTypeInfo()->convert(id).get() );

I don't know if it makes sense this way... Perhaps someone could point me in the right direction :)