When qutebrowser starts, it creates an in-memory sqlite database. One
can instantiate a SqlTable to create a new table in the database. The
object provides an interface to query and modify the table.
This intended to serve as the base class for the quickmark, bookmark,
and history manager objects in objreg. Instead of reading their data
into an in-memory dict, they will read into an in-memory sql table.
Eventually the completion models for history, bookmarks, and quickmarks
can be replaced with SqlQuery models for faster creation and filtering.
See #1765.
