Update VE core submodule to master (6c2c474)

New changes:
8cab432 ve.ui.AnnotationInspector: Allow content insertion without annotating
f5cbd05 ve.ui.AnnotationInspector: Stop truncating fragments to 255 elements
13d9f5e Update OOjs UI to v0.1.0-pre (dd294dc785)
50c4efd Set a default language for ve.dm.Document if we can't guess it otherwise
b28f2f1 Disable tools other than links and references on mobile

Change-Id: Ib4178c3c7e67135806046decff0bde05a2702f7d