CppTools: Locator: Match also against qualified names

If the user input contains "::", match against the qualified symbol
name. Otherwise, as before, match against the unqualified symbol name.

This applies to the function and class filters and allows to narrow down
the results by using a namespace prefix, e.g. "c core::*category".

Change-Id: Id152f412740e27f2f2d001dc7008dba8a92a37ce
Reviewed-by: David Schulz <david.schulz@digia.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>