Cache the results of has_jpeg_support and has_png_support
Cache the results of has_jpeg_support and has_png_support

This means we can use them on the admin dashboard without performing redundant file/image operations.

serzans/wagtail,kurtw/wagtail,hamsterbacke23/wagtail,takeflight/wagtail,nilnvoid/wagtail,rsalmaso/wagtail,kurtw/wagtail,FlipperPA/wagtail,wagtail/wagtail,nimasmi/wagtail,wagtail/wagtail,chrxr/wagtail,gogobook/wagtail,inonit/wagtail,davecranwell/wagtail,mixxorz/wagtail,zerolab/wagtail,serzans/wagtail,FlipperPA/wagtail,hanpama/wagtail,rsalmaso/wagtail,inonit/wagtail,zerolab/wagtail,davecranwell/wagtail,wagtail/wagtail,rsalmaso/wagtail,Toshakins/wagtail,gogobook/wagtail,gogobook/wagtail,takeflight/wagtail,hamsterbacke23/wagtail,kurtrwall/wagtail,kurtw/wagtail,nimasmi/wagtail,thenewguy/wagtail,kaedroho/wagtail,gasman/wagtail,nutztherookie/wagtail,kaedroho/wagtail,nealtodd/wagtail,chrxr/wagtail,quru/wagtail,jnns/wagtail,nealtodd/wagtail,iansprice/wagtail,kaedroho/wagtail,davecranwell/wagtail,nilnvoid/wagtail,Tivix/wagtail,Toshakins/wagtail,mikedingjan/wagtail,thenewguy/wagtail,quru/wagtail,gasman/wagtail,rsalmaso/wagtail,wagtail/wagtail,kurtrwall/wagtail,JoshBarr/wagtail,hanpama/wagtail,torchbox/wagtail,Tivix/wagtail,gasman/wagtail,JoshBarr/wagtail,nutztherookie/wagtail,thenewguy/wagtail,quru/wagtail,takeflight/wagtail,timorieber/wagtail,JoshBarr/wagtail,nutztherookie/wagtail,inonit/wagtail,gogobook/wagtail,serzans/wagtail,nilnvoid/wagtail,iansprice/wagtail,kaedroho/wagtail,hamsterbacke23/wagtail,nimasmi/wagtail,quru/wagtail,inonit/wagtail,mikedingjan/wagtail,nealtodd/wagtail,timorieber/wagtail,Toshakins/wagtail,jnns/wagtail,jnns/wagtail,thenewguy/wagtail,zerolab/wagtail,mixxorz/wagtail,nutztherookie/wagtail,torchbox/wagtail,hamsterbacke23/wagtail,gasman/wagtail,FlipperPA/wagtail,chrxr/wagtail,zerolab/wagtail,kurtrwall/wagtail,serzans/wagtail,jnns/wagtail,wagtail/wagtail,FlipperPA/wagtail,Tivix/wagtail,zerolab/wagtail,iansprice/wagtail,torchbox/wagtail,thenewguy/wagtail,kaedroho/wagtail,mixxorz/wagtail,Tivix/wagtail,chrxr/wagtail,JoshBarr/wagtail,Toshakins/wagtail,kurtw/wagtail,hanpama/wagtail,mikedingjan/wagtail,takeflight/wagtail,nealtodd/wagtail,mixxorz/wagtail,timorieber/wagtail,mixxorz/wagtail,kurtrwall/wagtail,rsalmaso/wagtail,torchbox/wagtail,nimasmi/wagtail,iansprice/wagtail,hanpama/wagtail,timorieber/wagtail,davecranwell/wagtail,gasman/wagtail,mikedingjan/wagtail,nilnvoid/wagtail