Fix yet more TODOs

[benjie]

• Key packages get a version export that's autogenerated at versioning time (removes require('../package.json').version hack)
• Uses a new more accurate parser for database identifiers from smart comments/tags
• Enable marking relations as @notNull
• Move attribute logic from PgConditionArgumentPlugin to PgAttributesPlugin
• Possible to set the modifier of an argument type via @arg0modifier smart tag
• Fixes a bug in PgFakeConstraintsPlugin where the fake constraint was added in the wrong place
• Updates PgIntrospectionPlugin to leverage more of pg-introspection (i.e. remove duplicate code and leverage the memoization pg-introspection offers)
• Fix the behaviors used in a few places