Locator: Allow to filter for path in BaseFileFilter

If the input contains a path separator, the input is matched against the
file path. Otherwise, as before, the input is matched against the file
name.

This affects AllProjectsFilter, CurrentProjectFilter and
DirectoryFilter.

Usage Examples:
    "src/*main.cpp"
    "cppedtior/"

Change-Id: I8bc55642b388a8f8e1d7a949f80bbe1abc41ae3c
Reviewed-by: hjk <hjk121@nokiamail.com>