Search Improved ranking and cross topic search

The reason for this PR is:
[#459]
https://github.com/geoadmin/mf-geoadmin3/issues/886

In this PR:
- Improved ranking by adding sentence match at the beginning and at the end (more importance to sentence matching where order matters). It fixes also the weighting issue with the new instance.
- Cross topic search in layers is now possible. By using "all" as a topic...
- Some code cleanup

All integration tests and ranking tests are green.