refs #21622 [finc] VuFind 6.1.2 templates upgrade

* remove some classnames
* corrects and updates add-to and remove-from cart buttons
* adds corresponding SCSS according to new file structure
* corrects class and adds alphabrowse in footer
* updates header theme button
* clarifies comment in checkbox.phtml
* upgrade footer, header
* upgrade /ajax/
* upgrade /cart
* upgrade /collection/
* upgrade /ContentBlock/
* upgrade /Helpers/
* upgrade /layout/
* upgrade /librarycards/
* upgrade /myresearch/
* upgrade /record/
* upgrade /RecordDriver/DefaultRecord/
* upgrade /RecordDriver/RecordTab/
* upgrade /RecordDriver/search/advanced/
* upgrade /RecordDriver/search/controls/
* upgrade fix bug in single-facet
* upgrade /search/

co-authored by: Claas Kazzer <kazzer@uni-leipzig.de>
* corrects short php tags, clarifies search-history and facets
* upgrade-related post-fixes
* corrects code in finc-acc. for upgrade