applets/systemtray: Consolidate config pages
Reason for the change
Right now it has two pages with contents that want different amount of space. As a result, there's no good window size that doesn't make one of the pages look ridiculous. The Entries page is also slightly hidden.
To alleviate this, merge the two pages together. Now there's one, it wants to be large, it looks good when large, and everything is discoverable.
Test plan
Open the System Tray config window, play with the settings.
Screenshots or screen recordings
| Before, "General" page | Before, "Entries" page | After, combined page |
|---|---|---|
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