Add a with_library_path scope to Attachable

[MSchmidt]

Context

I'm working on markdown support for Spina. To show images from the library I want them to be included with this easy syntax: ![Alt](foldername/imagename) within the markdown.

Changes proposed in this pull request

This scope on Attachable helps to fetch the right images based on that syntax.

Guidance to review

Right now Spina doesn't use this scope internally. So I can see how this might not be accepted at the time. Also it's still using ILIKE because that's what the main branch does. Will change it once you merge the sql PR.

[Bramjetten]

That's really really cool! Are you also looking at including a Markdown-editor (with preview?).

Really like the folder syntax.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Bramjetten]

Not stale!

how would House (MD) fit into this?

[MSchmidt]

House is not released yet, but I guess as trix alternative for the MD Parts it would work great. We'd need to expend it with an spina image picker though. This PR is only the preparation for that.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[MSchmidt]

@Bramjetten I'm not planning to add anything to this specific PR. It's mergeable as it is though. If you feel like this method should not exist on its own feel free to close it.