WvDbi split into multiple classes, and now parses URL-style database names.

WvDbi split into multiple classes, and now parses URL-style database names.

The MSSQL-specific and ODBC-specific parts are now in their own classes.
You can now create a WvDbi using a moniker by calling
WvDbi.create("whatever"), and the monikers can be either the old-style ones
or fancy new URL-style ones: mssql://user:password@host/database, or
odbc:MySQL://user:password@host/database.

To do: add a real mysql moniker to avoid the weird odbc:MySQL syntax.  Add
shortcuts so you don't have to enter your username and password all the
time.  Update versaplexd to construct its database connections using WvDbi
so that we can really take advantage of this.  Make a WvDbi descendant that
does queries via versaplexd, thus completing the abstraction.