Remove old search index and v0.10.x (flask) API, also clean the CLI

We will hardfork NOMAD and run v1.0.0 on new databases that will not support the old search index (and therefore most of the old flask API).

• remove v0 search and unify the search module once again
• remove the old metainfo search extension that drove the v0 index
• remove all of the old v0 API and its tests
• remove obsolete commands from client CLI (mirror, statistics?)
• migrate the integrationtests to v1 API
• migrate upload CLI to v1 API
• migrate local CLI to v1 API
• migrate aflow update to v1 API
• migrate uploads CLI to v1 search
• migrate Optimade API
• migrate dcat API
• migrate client.py to v1 API
• move lots of tiny API functions to v1 (done in #607 (closed))
• temporarily add the old edit API to v1 (done in #607 (closed))
• migrate all examples to requests and v1 API
• remove .dft (and other domains)
• remove nomad.cli.client.legacy._create_client
• "test" the GUI after refactors
• test the deployment

This depends on #588 (closed) and #607 (closed).