Add filtering to docType selection overlay

[dnwhte]

What it says on the tin.

[leekelleher]

Oooo, thank you @dnwhte! I'll review this in the coming days.

[leekelleher]

I've take a look at this, I'm liking it. Although I'm tempted to make it as a configurable option in the prevalue fields. As it'll be great for when there's a long list of Doc Types, but if there are a few, I don't think it's necessary. I'll take a look to see how this might work.

[leekelleher]

@dnwhte I've updated this PR with the config option, (in the Data Type settings).

However it will require a small tweak to Stacked Content to make it work, since the prevalues are only passed to the property-editor, not the overlay directly. So SC will need to pass in the enableFilter value.

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Here's the commit on Stacked Content: umco/umbraco-stacked-content@24edb59

[leekelleher]

@mattbrailsford Did you want to take a look at this? I'm happy for it to be merged in.

[leekelleher]

@mattbrailsford Here's a screengrab of the filter...

[leekelleher]

Merged in, thanks @dnwhte! 🎉