* backend: initial tags api support (addresses #365):
- add 'tags' field to crawlconfig (array of strings)
- allow querying crawlconfigs to specify multiple 'tag' query args, eg. tag=A&tag=B
- add /archives/<aid>/crawlconfigs/tags api to query by distinct tag, include index on aid + tag
tests: add tests for adding configs, querying by tags
tests: fix fixtures to retry login if initial attempts fails, use test seed of https://webrecorder.net instead of https://example.com/
7b5d82936d