Currently active Fedora is 29

The reason is that we want to profit from latest security updates and
therefore not use a copy of the SQLite3 source code that becomes outdated.

ToDo: test on different Linux distributions / bc2 and adapt compile
instructions accordingly, also container recipes must be adapted.

Changes in e9384a9f must be also
applied on calls to boost::python::eval

Tested with Boost 1.53 on CentOS 7.5 so it still works with old Boost.

- Introduced max_mappings_extensive attribute in QSscorer to control limit of
  checks to do in (slow) extensive chain mapping algorithm.
- Added qs-max-mappings-extensive command line flag to compare-structures to
  set QSscorer.max_mappings_extensive
- Clean error handling for failures in chain mapping in compare-structures