Improve vertical rhythm

[shawnbot]

This is an attempt to clean up after some of the changes in #106 degraded a couple of our live forms. (The form I'm looking at has some design problems in the form spec itself, but those will be harder to fix, IMO.) The proxy preview continues to be useful for testing, and for longer forms I've improved the panel component templates so that we can use renderMode: 'flat' to force the form out of "wizard" mode and see everything at once. Links to test:

• The live form, using formio-sfds v6.2.1 as of this writing
• Proxy preview of v6.3.1 to demonstrate the spacing issues
• Proxy preview of this PR
• Standalone preview of this PR
• "Flat" preview of this PR

/cc @aekong @nlsfds

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[github-actions[bot]]

Size Change: -60 B (0%)

Total Size: 91.6 kB

Filename	Size	Change
dist/formio-sfds.css	14 kB	-20 B (0%)
dist/formio-sfds.standalone.js	67.4 kB	-40 B (0%)

ℹ️ View Unchanged

| Filename | Size | Change | | |:--- |:---:|:---:|:---:| | `dist/common.css` | 484 B | 0 B | | | `dist/examples.js` | 3.71 kB | 0 B | | | `dist/examples/example.js` | 683 B | 0 B | | | `dist/portal.js` | 5.39 kB | 0 B | |

_{compressed-size-action}

[aekong]

renderMode: 'flat'! 🎉