Use project extent instead of WMS extent ...

[saberraz]

This page:
https://merginmaps.com/docs/tutorials/further-project-customisation/#project-extent
should be updated to use project extent:
MerginMaps/mobile#1762

[PeterPetrik]

add also to: https://merginmaps.com/docs/field/input_ui/#zoom-to-project
maybe also: https://merginmaps.com/docs/layer/best-practice/

maybe change section name in tutorial to have also "zoom" keyword so it is possible to search for.

[wonder-sk]

maybe not very clear from pull requests where is the right place where project extent can be set, it's here: