Changes

SQLite: remove indices that are prefixes of others

This follows the advice in the official SQLite docs [1]:

  Hence, a good rule of thumb is that your database schema should never contain
  two indices where one index is a prefix of the other. Drop the index with
  fewer columns. SQLite will still be able to do efficient lookups with the
  longer index.

[1]: https://www.sqlite.org/queryplanner.html#_multi_column_indices

Refinements to model-driven SQLite backend in preparation for time-aware version

ITimeAwareGraphNode: instants use long values

core: EOLQueryEngine is autocloseable

SVN history test: avoid compilation warning

[LARGE] Add time-aware version of SQLite backend