Proposal: Simplify tectonic region for user defined logic trees

[chrisdicaprio]

Background

The tectonic_region_type and tectonic_region_types are fields of GMCMBranch and SourceBranch. For a particular BranchSet these fields must mach.

Problem

If a user were to hand-build a logic tree, this requires a lot of redundant fields to be hand-entered which is both tedous and error prone

Solution

We want to modify serialization and de-serialization of LogicTrees such that the tectonic region type fields can be defined at the branch set level for ease of use. Actual implimentation of the class is to remain with the fields on the branches. This is needed due to how combined branches are used in toshi-hazard-post