Tracking Issue: MultiVector

[MarcelKoch]

This is a tracking issue for the proposed addition of a (multi-)vector interface. It keeps track off the related PR and how they build on top of each other.

PRs:

• Multivector interface #1889
• 1888/implicit conversion #2039
• Dense MultiVector Implementation #1890
• Distributed Vector MultiVector Implementation #1891
• 1888/remove linop hierarchy #2040
• 1888/renaming #2041
• 1888/dense linop #2042
• MultiVector Usage Test #1892

Todos:

• add precision stuff to batched