Sample is_control

[MatthewMah]

The current implementation checks only the control letter. This is mostly correct. Newer controls do not bother to create fake samples.

The problem arises from collaborator products (at least extracts) sent that were processed normally and given sample numbers. Some of these are actually controls, for example: S25321.

Proposal:
Validate sample by checking that all layout elements corresponding to a sample at all stages (lysate, extract, library, capture) agree on control type.
Compute by returning control type of any layout element.