Remove the smart picker modal padding

[julien-nc]

• Remove it to let custom picker components set it if needed.
• Adjust the padding of the generic search.
• Make one class more explicit

This allows, for example, custom picker components that have infinite scrolling (like the Giphy integration one) to remove bottom padding/margin which looks better.

As we can't make sure nextcloud/vue is updated everywhere at once and all the providers are adjusted (I'll make sure most of them are 😁 ), we might temporarily have:

• double padding with adjusted providers displayed in apps using an old nextcloud/vue release
• no padding at all for old providers displayed in apps using a nextcloud/vue release which includes those changes

Not that bad IMO.

[mejo-]

@julien-nc seems sensible to me. Could you provide a (non-comprehensive) list of apps with picker componenents that are not under your umbrella? 😬

[julien-nc]

@mejo- Thanks for the review. So far I'm not aware of many providers implementing a custom picker component.
Appart from mines, there is the Files one implemented by @juliushaertl and that's about it I think.