Inject the database service into SQL

Currently Views has a few of Database::getConnection() calls without specifying target or key and so non-default databases are not supported properly.

We could solve this easily by injecting a database connection which is on the roadmap:

1. #1935300: Thou shall not hardwire Database in your filters migrate everything relevant into the Sql class
2. #1934448: Clean up a little Views date handling/arguments this too
3. #1863816: How to make plugins receive injected objects from the container ? will allow us to inject the new database service into Sql and as per 1. and 2. that's the only place where any interaction with the database happens.