Revert Manage Themes dialog group/theme name input change

[macintoshhelper]

Why does this PR exist?

Fixes #2880

What does this pull request do?

Testing this change

1. Go to the Manage Themes modal by clicking Theme: None or Theme: {theme_name_here}
2. Click Manage Themes
3. Click the + New Theme button
4. Check visually that the new UI is being used
5. Try entering a group name and theme name

Additional Notes (if any)

• Also fixes a bug around empty group name populating the input when renaming the group name
• Added text input placeholders for Add group and Theme name

Before	After

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Latest commit: dd4bc77c82dbf0e3fd096eaa9045e94252e5e96f

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[six7]

@macintoshhelper would you want to make these changes in a follow-up PR? I'll merge this in for rc8 given the requested changes dont change behavior too much 👍