Predicates: inconsistent docs & code regarding isProperty & isLiteral

[steveschmitt]

This is about how to tell Breeze whether the object of a Predicate is a property name or a literal.

The Query using JSON doc says use the isProperty flag.

The Querying in depth doc says use the isLiteral flag.

The code comments in predicate.ts 77 says to use isLiteral.

The actual code in predicate.ts 937 says to use isProperty.

We need to change it to isProperty everywhere, I think, but we need to find out why we thought it was isLiteral at one point. Did this change from Breeze 1.x to 2.x?

Related to #73.