refs #17752 [finc v5] handle cover and style based icons

* reset to original operating mode: first cover, then style based icons
** Default core
** SolrAI core
** SolrMarc core
* but if cover cannot be loaded, then use style based icon as fallback
** by using object tag with inner icon
** by setting content of fallback icon noCover2 to empty => interpreted as no content in browser

* add new fallback icon instead of changing existing

** keep noCover2.gif unchanged, but add new empty file noCoverEmpty.gif
** use noCoverEmpty.gif in finc as default noCoverAvailableImage set in config.ini
** after merging this branch, instances won't have a noCoverAvailableImage anymore:
*** either set noCoverAvailableImage = images/noCover2.gif in instance config.ini
*** or use object tag in core templates as in master core templates

co-authored by: "ckaz <kazzer@uni-leipzig.de>"
refs #17752 [finc vf5] fixes record view icon placement

* fixes record view icon placement for left-aligned facets in
** DefaultRecord/core
** ...