Clang-format can't really handle the doxygen tags with a blackshlash.
Therefore, replace them with the @-prefix.

Add CI job, to check for consistency, but allow it to fail, to prevent
false positives. Let's observe it for a bit, and then we can change it
later.

Nikola Dinev authored Jan 12, 2020 and Tobias Lasser committed Jan 12, 2020

- add BlockLinearOperator to operators
- add block descriptors (IdenticalBlockDescriptor, PartitionDescriptor, RandomBlocksDescriptor) and made BlockDescriptor abstract

Nikola Dinev authored Dec 06, 2019 and Tobias Lasser committed Dec 06, 2019

Protect copy constructors in non-leaf and leaf classes, to avoid the implicitly generated ones by the compiler that could cause slicing. In Cloneable, the assignment operator was deleted to disable issues with implicitly generated assingment operators in derived classes to prevent slicing. (resolves #31)