Add sql database impl of MessageStore

Created by: mgatny

• New session settings: SQLDriver and SQLDataSourceName
• Uses the sql pkg directly (no external deps)
• The DDL files in _sql/ are borrowed from quickfix/c++ and quickfix/j
• Only tested with sqlite3 driver so far
• Should work with the mysql driver (will probably need parseTime=true in the DSN)
• It may be useful going forward to have separate mysql, sqlite, postgresql, etc. impls of sqlStore to work around the differences (e.g. DATETIME parsing and ? vs $1 in prepared statements)

Refs #88 (closed)