theme.json: Default location changed to THEME/Config/theme.json

THEME/webroot/theme.json is still supported but deprecated

Closes #533
Add Block method + teach Blocks to use it
Teach filterBlockShortcode to use new RegionsHelper::block method
Add tests for block() method
Consistent code formatting across test methods
Merge branch 'pr/527' into 2.0

* pr/527:
  Consistent code formatting across test methods
  Add tests for block() method
  Teach filterBlockShortcode to use new RegionsHelper::block method
  Add Block method + teach Blocks to use it

Closes #527