Feature request: Add a bottom preview pane.

[chipzhang]

Checklist

• [X] I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• [X] I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• [X] I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• [X] I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
• [X] This issue contains only one feature request.
• [X] I have read and understood the contribution guidelines.
• [ ] I optionally donated to support the Fossify mission.

Feature description

Add an option to display a bottom preview pane. So that, when viewing a photo in non full screen mode, it displays a pane in the bottom, with the thumbnails of all pictures in the current album. And the user can click the thumbnail to quickly switch to the desired photo.

Why do you want this feature?

If there are too many photos in an album, the user can scroll the bottom preview pane, and click the thumbnail to switch to another photo more quickly. No need to press back button to go to the thumbnail list view first.

Additional information

If anyone wants to know more about what this feature is, Aves Gallery app has this feature. You can install it (available in Play and Fdroid), then go to Settings -> Viewer -> Overlay -> check 'Show thumbnails', then close the settings, and open a photo in an album, and a bottom preview pane appears.