Make all gallery images the same dimensions.

Signed-off-by: Marios Sotiropoulos <mai1211@uom.edu.gr>
Adjust the image slider styles to the gallery image dimensions.

Signed-off-by: Marios Sotiropoulos <mai1211@uom.edu.gr>
Remove references of unused files from the "slideshow.html.twig" template.

Signed-off-by: Marios Sotiropoulos <mai1211@uom.edu.gr>
Enable the Symfony caching mechanism.

Signed-off-by: Marios Sotiropoulos <mai1211@uom.edu.gr>