Allow the user to create a new tag using `neuron--select-tag-from-query'

[pjones]

If the user enters a tag name that does not exist ivy-read will return it, but then get-text-property will return nil. In that case just return the user-entered text.

[felko]

Good idea, thank you. I believe neuron--select-tag-from-query should rather take an optional require-match argument that controls this behavior, because in some cases (e.g. in neuron-query-tags) we actually want the user to select an existing tag. Also, I was thinking maybe entering a new tag could reload the zettel cache?

[pjones]

Good ideas. I'll update this PR.

[pjones]

@felko I added the require-match argument and the cache rebuild.

[felko]

Thank you!