Combine lexicon id and version in schema

[goodmami]

In trying to reduce stateful entities (see #226), I find myself replacing a lot of rowid conditions in SQL queries with id || ":" || version (since lexicons have a unique id + version pair in the database, it serves as a unique identifier). It occurs to me that it would be more efficient to just have the concatenated id:version ("lexicon specifier") as a single, indexed column in the database. With SQL globs we can find lexicons only by their id (id:*) or version (*:version), so there shouldn't be any loss of functionality.

This change would require databases to be rebuilt.