Fix various metadata editor issues

[gordlin]

Related Item(s)

Issues:
#444
#449

Changes

• [Field labels have inconsistent captialization #444] Changes all subheadings in metadata form to Sentence case.
• [Easier way to edit opposite language metadata in the editor #449] Adds config language swap button to Edit Metadata modal.
• Prevents duplicate/incorrect toasts from showing up on metadata editor screen when no UUID entered/UUID doesn't exist.
• Makes minor styling modifications to editor Table of Contents.

Testing

Steps:
#444:

1. Go to the Create new product screen, and scroll down to the metadata details form.
2. See that all headings are now in sentence case.

#449:

1. Open any product, and navigate through to the editor.
2. Click the Edit Metadata button in the sidebar.
3. You should see a View English/French Config button, allowing you to swap to the metadata for the other language.

Other:

1. Back on the Load Existing Storylines Product page, ensure the UUID is blank and press "Load". You should only get ONE toast, telling you to enter a UUID first (before, you'd get multiple, with some saying that UUID "" doesn't exist).
2. Enter a non-existant UUID. You should get ONE toast notifying you the UUID doesn't exist.
3. Enter a UUID that exists. The form should pop up as expected.

---

This change is 

[github-actions]

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

[szczz]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @gordlin)

[IshavSohal]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @gordlin)

[RyanCoulsonCA]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @gordlin)

[yileifeng]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @gordlin)