Add sanitization/validation function for ISA-create mode (e.g. Datascriptor)

[Zigur]

We need some sanitization/validation on study design JSON configs submitted to the rest service.
In brief, these are the checks performed

• each arm has subject size < MAX_SUBJECT_SIZE = 1000
• there are no more than MAX_ARMS = 20
• each sample type in the sample plan produces no more than MAX_SAMPLE_SIZE = 10000 (this is computed as subject_size *sample_size)
• the combinatorial output of the protocol parameters for each assay must not exceed MAX_ASSAY_COMBINATIONS = 32

If the validation is passed the function returns None. Otherwise, it returns a dict outlining all the checks that are not passed.

The returned messages are open to improvements.