Add modified property to dynamic panel schema, Fix SVG rendering

[IshavSohal]

Related Item(s)

#456
#436

Changes

• Add modified property to the dynamic panel schema
• Convert svgs to text rather than blob, so that they are correctly rendered in the editor and preview

Testing

Steps (#436):

1. Edit an existing product and change the logo to an svg (can use
   git-bash)
2. Load the product into editor-main
3. Click the Edit Project Metadata button, and observe that the svg logo is correctly displayed
4. Upload the svg to an image panel, switch to a different slide and switch back to the image panel
5. Observe that the svg is correctly displayed
6. Open the preview
7. Observe that the svg logo and the svg in the image panel are correctly displayed,

Steps (#456)

1. Make a new slide with a dynamic panel
2. Create an image panel and upload an image
3. Go to advanced editor and there should be no schema error

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This change is 

[github-actions]

Your demo site is ready! 🚀 Visit it here: https://ramp4-pcar4.github.io/storylines-editor/issue-456

[szczz]

Looks good to me, and I agree with the index.js changes but should they be part of this PR?

Reviewed 8 of 8 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @IshavSohal)

[RyanCoulsonCA]

I'm noticing that if you paste a link to an external SVG (the git-bash one you linked, for example) and then proceed to the main editor, nothing will load and you'll notice a CORS error in the console. This doesn't need to be fixed in this PR, but we should open a new issue to investigate this.

Reviewed 8 of 8 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @IshavSohal)

[yileifeng]

^ If fix not complicated would be great to include in this PR, if takes too long new issue is good

Reviewed 8 of 8 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @IshavSohal)

[gordlin]

Reviewed 8 of 8 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @IshavSohal)