Make permission checks namespace safe

[yippie]

Fixes #153

Fixes an issue where including trigger action framework in a namespaced package makes custom permission checks fail if the permission is not in the same namespace.

This requires using 2 SOQL queries to connect the User to the Custom Permission. To minimize the number of queries and processing done, the following strategies were employed:

• Blindly get ALL custom permissions assigned to the user instead of parsing through the actions and pulling out permissions to check one at a time. Then, when checking permissions, simply check if the permissions list contains the desired permission. The allows the queries for user permissions to happen exactly once.
• Move permission checks to a dedicated, static class, that can cache and share the permission with all handlers, including finalizers, that happen in a transaction context.

Unit tests were updated to mock permissions the new way but were otherwise untouched as the goal of this change is to cause zero change in behavior or functionality.

• Tests pass
• [N/A no behavior change] Appropriate changes to README are included in PR

[dschach]

Curious why using isNOTBypassed - it can be confusing to the user/dev if Booleans are expressed negatively.

Gentle suggestion: Update to isBypassed and return the negative of the output (which is already a negative, I see).