Cleaned up page validation
Cleaned up page validation

Previously, we added an extra validation rule to the slug field by overriding the clean_slug method on the page, which was a little hacky I think.

This PR removes this code and uses form.add_error instead (added in Django 1.7) for performing the extra validation rules.

nilnvoid/wagtail,rjsproxy/wagtail,taedori81/wagtail,iho/wagtail,jnns/wagtail,JoshBarr/wagtail,hanpama/wagtail,mixxorz/wagtail,jordij/wagtail,gasman/wagtail,inonit/wagtail,zerolab/wagtail,tangentlabs/wagtail,FlipperPA/wagtail,jnns/wagtail,nimasmi/wagtail,kaedroho/wagtail,iansprice/wagtail,hamsterbacke23/wagtail,nutztherookie/wagtail,rsalmaso/wagtail,nilnvoid/wagtail,nilnvoid/wagtail,WQuanfeng/wagtail,rv816/wagtail,nimasmi/wagtail,m-sanders/wagtail,marctc/wagtail,WQuanfeng/wagtail,bjesus/wagtail,iho/wagtail,takeflight/wagtail,jnns/wagtail,nilnvoid/wagtail,davecranwell/wagtail,rv816/wagtail,nealtodd/wagtail,KimGlazebrook/wagtail-experiment,m-sanders/wagtail,jordij/wagtail,rv816/wagtail,kurtrwall/wagtail,bjesus/wagtail,Pennebaker/wagtail,Tivix/wagtail,quru/wagtail,iansprice/wagtail,nealtodd/wagtail,inonit/wagtail,JoshBarr/wagtail,thenewguy/wagtail,marctc/wagtail,KimGlazebrook/wagtail-experiment,darith27/wagtail,torchbox/wagtail,nutztherookie/wagtail,nrsimha/wagtail,nimasmi/wagtail,takeshineshiro/wagtail,serzans/wagtail,davecranwell/wagtail,iho/wagtail,takeshineshiro/wagtail,janusnic/wagtail,serzans/wagtail,mixxorz/wagtail,Toshakins/wagtail,nrsimha/wagtail,hanpama/wagtail,wagtail/wagtail,rsalmaso/wagtail,Pennebaker/wagtail,kurtw/wagtail,taedori81/wagtail,mephizzle/wagtail,JoshBarr/wagtail,KimGlazebrook/wagtail-experiment,rv816/wagtail,mjec/wagtail,mephizzle/wagtail,Toshakins/wagtail,tangentlabs/wagtail,taedori81/wagtail,jordij/wagtail,gogobook/wagtail,mayapurmedia/wagtail,Klaudit/wagtail,Klaudit/wagtail,quru/wagtail,rjsproxy/wagtail,mayapurmedia/wagtail,mephizzle/wagtail,m-sanders/wagtail,Tivix/wagtail,tangentlabs/wagtail,marctc/wagtail,nutztherookie/wagtail,hanpama/wagtail,kaedroho/wagtail,gasman/wagtail,tangentlabs/wagtail,torchbox/wagtail,mikedingjan/wagtail,inonit/wagtail,WQuanfeng/wagtail,kurtrwall/wagtail,stevenewey/wagtail,taedori81/wagtail,Klaudit/wagtail,jnns/wagtail,nimasmi/wagtail,takeflight/wagtail,Klaudit/wagtail,bjesus/wagtail,FlipperPA/wagtail,zerolab/wagtail,rjsproxy/wagtail,torchbox/wagtail,chrxr/wagtail,janusnic/wagtail,darith27/wagtail,wagtail/wagtail,bjesus/wagtail,serzans/wagtail,kaedroho/wagtail,gogobook/wagtail,hamsterbacke23/wagtail,chrxr/wagtail,mixxorz/wagtail,mjec/wagtail,timorieber/wagtail,hanpama/wagtail,quru/wagtail,rsalmaso/wagtail,kaedroho/wagtail,rsalmaso/wagtail,mixxorz/wagtail,stevenewey/wagtail,mikedingjan/wagtail,wagtail/wagtail,mayapurmedia/wagtail,timorieber/wagtail,wagtail/wagtail,inonit/wagtail,gasman/wagtail,janusnic/wagtail,timorieber/wagtail,gasman/wagtail,Pennebaker/wagtail,mjec/wagtail,Toshakins/wagtail,Toshakins/wagtail,FlipperPA/wagtail,kurtrwall/wagtail,hamsterbacke23/wagtail,jordij/wagtail,kurtrwall/wagtail,mikedingjan/wagtail,timorieber/wagtail,marctc/wagtail,gogobook/wagtail,davecranwell/wagtail,iho/wagtail,takeflight/wagtail,nrsimha/wagtail,thenewguy/wagtail,nealtodd/wagtail,stevenewey/wagtail,mephizzle/wagtail,takeshineshiro/wagtail,serzans/wagtail,nutztherookie/wagtail,kurtw/wagtail,zerolab/wagtail,taedori81/wagtail,gogobook/wagtail,mikedingjan/wagtail,thenewguy/wagtail,FlipperPA/wagtail,rjsproxy/wagtail,takeshineshiro/wagtail,thenewguy/wagtail,chrxr/wagtail,kurtw/wagtail,kaedroho/wagtail,zerolab/wagtail,davecranwell/wagtail,mayapurmedia/wagtail,Tivix/wagtail,nealtodd/wagtail,torchbox/wagtail,chrxr/wagtail,WQuanfeng/wagtail,stevenewey/wagtail,JoshBarr/wagtail,m-sanders/wagtail,zerolab/wagtail,darith27/wagtail,rsalmaso/wagtail,thenewguy/wagtail,KimGlazebrook/wagtail-experiment,iansprice/wagtail,takeflight/wagtail,quru/wagtail,iansprice/wagtail,mjec/wagtail,gasman/wagtail,nrsimha/wagtail,hamsterbacke23/wagtail,mixxorz/wagtail,Pennebaker/wagtail,Tivix/wagtail,wagtail/wagtail,kurtw/wagtail,janusnic/wagtail,darith27/wagtail