merge trails function added (#627)
* merge trails function added
* fix conflict resolve issues
* avoid incorrect authorship when merging trail comments
* require edit access for all selected trails before merge
* fix likes checkbox binding in trail merge modal
* improve error handling
* require editable target and deletable sources for merge
* avoid duplicate trail fetch during merge
* prevent duplicate likes when merging trails
* check photo download responses during trail merge
* add merge completion toast notifications
* cleanup
* small fixes
* move merge code to backend, option to merge single trail selection with similar one, automatic merge for integrations add as option, maintenance page to find and merge similar trails added
* fix build error
* fix
* docu, beautifying, refactoring
---------
Co-authored-by: Flomp <Flomp@users.noreply.github.com>
b5739cb72e