[analyzer] Refactor and simplify SimpleConstraintManager

Summary: SimpleConstraintManager is difficult to use, and makes assumptions about capabilities of the constraint manager. This patch refactors out those portions into a new RangedConstraintManager, and also fixes some issues with camel case, formatting, and confusing naming.

Reviewers: zaks.anna, dcoughlin

Subscribers: mgorny, xazax.hun, NoQ, rgov, cfe-commits

Differential Revision: https://reviews.llvm.org/D26061

llvm-svn: 296242