Working on fixing a bug in the database.

+ Added more tests.
+ Moved is_in_scope method to Data to simplify logic (and fix a bug).
+ Made the Database singleton easier to access (no longer having
to "instance" it).
+ Improved the test UI so it shows exceptions and warnings more clearly.
+ Now UrlVulnerability() sanitizes some bad but salvageable input.
Fixed database error.

The plugin bootstrap wasn't properly finding data
that was referenced but not returned.
Fixed message priority for errors and warnings.