Introduce parallel eigensolver using ScalaPACK or ELPA
Description
This function solves the eigenproblem in parallel for a non-distributed matrix. It transparently distributes the matrix, solves the problem in parallel and gathers the eigenvector matrix again.
For this, some more interfaces to pblas/scalapack functions are introduced.
The parallel eigensolver is called from one place in the Casida implementation right now.
News snippet
Introduce parallel eigensolver using ScalaPACK or ELPA
Checklist
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I have checked that my code follows the Octopus coding standards -
I have added tests for all the new features added in this request.