Avoid too many binding evaluations in the runtime

[Janpot]

Closes #2139

• evaluate all bindings only once per scope per render
• encapsulate runtime scope and set up a parent/child relationship. Basically we use the same primitives for local scope as we use for global scope
• update binding editor to understand scopes
• expand test suite with more test cases testing
  • access local from local
  • set local from local
  • access global from local
  • set global from local

Notes

• Why do textfields call onChange during mount?