Add scaling support of embedded page to ui-iframe node

[HiroyasuNishiyama]

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)

Proposed changes

This PR add scaling feature of embedded web page to ui-iframe node. An example of the new feature can be found in Import/Examples/node-red-node-ui-iframe/04 - Scale embedded web page.json.

Checklist

• [x] I have read the contribution guidelines
• [x] For non-bugfix PRs, I have discussed this change on the forum/slack team.
• [ ] I have run grunt to verify the unit tests pass
• [ ] I have added suitable unit tests to cover the new/changed functionality

[dceejay]

Published to npm - many thanks