Convert guide/editall page into a component

[kevinshen56714]

This PR converts content in guide/editall.html into the <chromedash-guide-editall-page> component. The changes include:

1. Created chromedash-guide-editall-page.js and chromedash-guide-editall-page_test.js
2. Slightly modified the template data of editall.html in guide.py so that the flat_forms can be passed into <chromedash-guide-editall-page> as string and then get JSON.parse() when rendering.
3. The guide/edit.html is now a single component file
4. Added loading skeletons for the page, see the snapshot below: