Optional Read/Write system parameters

[EdvinNilsson]

Reason

To create system that can have optional read/writes depending on if the component is on the entity.
For example, the rendering system could use default Rotation if there is no Rotation component on the entity.

Requirements

• There is a version for both Read and Write.
• The system parameter will return an Option with the Some reference or None.
• The system parameter matches any entity.

Dependencies

• Dynamic Archetypes #72