Add share extension

[koraykoska]

Fixes #81

I am using a "hack" by saving the shared video in an app container and opening the main application with the help of a WebView in the share extension view.
The share extension is closed once Gifski is opened. This is a little bit ugly right now as you can see the empty share extension for a few moments. I don't see another workaround as the WebView needs some time to open Gifski.
I added a simple CSS loading animation into the WebView so it doesn't look too ugly while loading, especially if the file shared is rather big and the copy process takes a few more moments.

The rest is handled by Gifski as it was always. The URL is opened and Gifski starts the Edit process.

---

IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #81: Share extension

---

IssueHunt has been backed by the following sponsors. Become a sponsor

[koraykoska]

@sindresorhus @sunshinejr

[koraykoska]

Btw, I am using the hack because share extensions are actually not made for things like opening the main application. They are more like for messenger apps sharing posts or something...

I saw that most non-messenger apps solve it like that so I guess it should be fine. Even if it is technically a hack...

[sindresorhus]

Why do you need the web view? There's https://developer.apple.com/documentation/foundation/nsextensioncontext/1416791-open

[koraykoska]

@sindresorhus The open function of NSExtensionContext cannot be used from a share extension. It's stated in the docs that only some extensions are allowed to use it. That's the reason for the WebView workaround

[sindresorhus]

Did you try the performSelector workarounds mentioned in https://stackoverflow.com/questions/24297273/openurl-not-work-in-action-extension and https://stackoverflow.com/questions/25727489/how-to-launch-a-parent-ios-app-from-its-app-extension ?

[koraykoska]

Ok NSWorkspace.shared.open works...i will delete the WebView stuff then...

[koraykoska]

@sindresorhus Done. I guess I got everything you mentioned.

[sindresorhus]

Can you mention the feature in the readme here: https://github.com/sindresorhus/Gifski#features

And also a quick guide on how to use it for screen recording purposes? As described in #81. Maybe in a Tips section.

[koraykoska]

@sindresorhus Done. I included the tip for the screen recordings directly into the features section. This is quite on the top of the readme, which is a great place for this feature.

[koraykoska]

@sindresorhus I am done with your suggestions. I think I didn't forget anything.

[sindresorhus]

Regarding #156 (comment), you could just present a simple error view with a text field and a OK button in ShareViewController.

[koraykoska]

@sindresorhus I changed it. The error will now be shown directly in the extension view and not redirected to the main app.

[sindresorhus]

Looks good to me now. Really nice work, @Ybrin 👍