Do not export databasesanitizer by default
Summary:
The interfaces of DatabaseSanitizer class and baloodb tool aren't fixed yet.
Make building them optional.
Reviewers: Baloo, davidedmundson
Reviewed By: davidedmundson
Subscribers: smithjd, Frameworks
Tags: Frameworks, Baloo
Differential Revision: https://phabricator.kde.org/D11657