Incorrect signature for activity functions

[abargnesi]

Activity terms result in an abundance return type. For example kinaseActivity's signature is defined as:

kinaseActivity(F:abundance)abundance

It is then valid to embed an activity term in another abundance:

# signature: complexAbundance(F:abundance...)abundance
complex(kin(p(HGNC:JAK2)))

This should not be semantically valid. The activity functions should instead return their function as a result to catch this type of error.

See OpenBEL/language#8.