(bug 43871 - bug 43872) New Special Pages to edit entities without
javascript

New baseclass "SpecialSetEntity" and subclasses "SpecialSetLabel",
"SpecialSetDescription" and "SpecialSetAliases"

patchset 16: rebased & resolved conflicts
patchset 17: adjusted selenium test for Special:SetLabel
patchset 23: SpecialSetSiteLink now depends on siteid instead of language
patchset 26: removed SpecialSetSiteLink (splitting)

Change-Id: Ib3650cf8cba0eb4014f33b27bfd07fba1a3b7767