V2.0 cleanup

[patrickjdanaher]

Items for V2.0 (protein compatibility) to be ready for launch:

• get_anchor_stats: don't insist on SDs unless assay_type = "protein"
• default everything to assay_type = "rna"
• add spatialUpdate()
• add function deriveProfiles() based on Estep()
• should "neg" be required if we're running protein? (If not, then make sure this is added to all exported functions. Default neg = NULL, then check it's not NULL if it's an RNA assay, and error informatively. If left as NULL for protein, shouldn't impact anything downstream.)
• fix bugs in issues