Migrating to v5

LNT v5 is a redesign of LNT whose database, REST API and web UI are not compatible with v4’s. Data held by a v4 instance is moved to a v5 instance in three steps: lnt mirror-v4 first copies the data of a v4 instance into a local directory through its REST API, lnt v5 convert-v4-mirror then converts that copy into v5 runs, and lnt v5 submit submits them to a v5 instance.