Merge tag 'v0.7.7' of github.com:cayleygraph/cayley into HEAD

ci: disable snap publish for now

iterator: do not drop an error in resolver

fix version for 0.7.4 release

graphql: update dependency and test filter with multiple values

bump version to 0.7.3

schema: allow to customize behavior; resolves #694

update dependencies

add v0.6.1 migration guide; mention dataset conversion in import docs

Tag v0.6.1 for release