Data type refactor

[timfelle]

Work on refactoring our data types. This work extends on the tensor system and unifies our array objects under a single umbrella. The array type implements storage, while specialised types create a pointer with the appropriate shape, matrix is 2D etc.

• Abstract array_t, the parent of all arrays. Linear storage and handles the common interfaces such as allocation, device synchronisation etc.
• Mathematical arrays moved to the array_t system. (vector, matrix, ... )
• Significant testing needs to happen to make sure we preserve performance.

Deferred to later work.

• Unify mathematical operations behind the shared type, keeping specialised operations separate (matrix inverse, etc).
• Then we can discuss moving field_t to the same underlying structure.

This PR depends on #2749 #2756