Add support for passing connection mode to sqlite3

[ysagal]

sqlite3 supports passing of "mode" on new connections:

new sqlite3.Database(filename, [mode], [callback])
mode (optional): One or more of sqlite3.OPEN_READONLY, sqlite3.OPEN_READWRITE and sqlite3.OPEN_CREATE. The default value is OPEN_READWRITE | OPEN_CREATE.
https://github.com/mapbox/node-sqlite3/wiki/API

I believe this can be handled by passing mode to dialectOptions and modifying this line to pass it on to the sqlite3 library:
https://github.com/sequelize/sequelize/blob/master/lib/dialects/sqlite/connection-manager.js#L33

[janmeier]

Sure, PR welcome :-)

[ysagal]

Okie dokie #4302