Move mobile templates to core app

--HG--
rename : wger/manager/templates/mobile/base.html => wger/core/templates/mobile/base.html
rename : wger/manager/templates/mobile/base_wide.html => wger/core/templates/mobile/base_wide.html
rename : wger/manager/templates/mobile/delete.html => wger/core/templates/mobile/delete.html
rename : wger/manager/templates/mobile/form.html => wger/core/templates/mobile/form.html
rename : wger/manager/templates/mobile/index.html => wger/core/templates/mobile/index.html
rename : wger/manager/templates/mobile/misc/contact.html => wger/core/templates/mobile/misc/contact.html
rename : wger/manager/templates/mobile/navigation.html => wger/core/templates/mobile/navigation.html
rename : wger/manager/templates/mobile/template.html => wger/core/templates/mobile/template.html
rename : wger/manager/templates/mobile/user/login.html => wger/core/templates/mobile/user/login.html
rename : wger/manager/templates/mobile/user/preferences.html => wger/core/templates/mobile/user/preferences.html
Fix language resource reference for exercise endpoint