Search: Add additional view type using pig.js

[seond]

This PR is to create a new feature that was requested in #85. The ask of issue #85 was to use pig.js to create a feed that is a lot easier to scroll through all the images with better performance. The result turned out pretty nice. The page loads 1500+ images I have almost instantly and I can freely scroll to any position of the huge stack of pictures, then the page fluently lazy load the requested part of the page smoothly.

Check this demo to see how smooth it is.
https://drive.google.com/file/d/1Gku6aWRzShX4Ciz3xg68XHIvDCGv_Y8v/view?usp=sharing

Here's a few implementation highlights:

• The page replicates the existing /photos page in terms of 1. how it handles the filters/url params 2. all the actions on an opened image
• Instead of infinite scroll mechanism, the page loads all the images that subject to the applied filter based on the batch size. API calls are made consecutively instead of being made simultaneously.
• The page creates multiple chunk divs as many as the number of batches then converts each div into a pig.js object so it can prevent a dom object from being humongous.
• The only event that could be handled on a photo item was onClick due to the limitation pig.js has. The library does not provide any other event handler options. You can still like and the rest of actions by opening the image by clicking on it.

The page is accessible at /instant and I intentionally skipped adding the page in the menu to leave it on to the maintainers to decide how we want to utilize or even improve/develop this page in a long run.

This is my first contribution to PhotoPrism and I fell in love with the project as I was trying and working on it. Great work, and big thanks to all the efforts on this fantastic project.

[lastzero]

Thank you very much for submitting this PR & sorry for the wait!

• Loading all search results is generally not a good idea as some users may have millions of pictures.
• Users trying different search filters / keywords are going to trigger many reloads.
• Results should automatically refresh after new files have been added / uploaded as well.

Loading all pictures is very inefficient in this case. It's great in case the user scrolls very far, doesn't change search filters, and there are no index updates. A solution might be to disable those features on this page and maybe also reduce the amount of metadata if the view doesn't need it, similar to Places.

The pig.js library should be included via NPM (see https://github.com/photoprism/photoprism/blob/develop/frontend/package.json) and not directly added to our repository.

[CLAassistant]

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[lastzero]

Thanks a lot for your contribution! I have to close this PR as there is still a lot of work to do and we haven't received any feedback for a long time. pig.js may be something we can use for a static export in the future though.