User should be able to easily create a new quick query for a given database

[aeisenberg]

Right now, you can have a single quick query per workspace. And the qlpack for the quick query is always by default the same language as the current database. There are really two pieces to this feature request:

1. Allow users to create a new quick-query file without clobbering the old one. There would be a new command CodeQL: Create new Quick Query, which will open a new file, named quick-query-n.ql where n is an increment number. Users can always manually rename the file if desired.
2. Allow user to update the generated qlpack to point to new languages.

The first point should be implemented. And the second one should be discussed. Maybe it's fine to force updates to the qlpack to be manual.