SUBMODULE UPDATE: facebook-ios-sdk. Fixes #771 - Facebook errors
NEW FEATURE: file share now has its own icon with file extension in SHKFormFieldCellLargeText
REFACTORING: Facebook now uses SHKFormFieldLargeText instead of SHKFormControllerLargeTextField
NEW FEATURE: SHKFacebook can autoshare. This can be globally switched off in configurator - Facebook sharer inherits default ShareKit behaviour, finally.
REFACTORING: removed config item SHKActionSheetSubclass, as this is exposed to host app and everybody can use his own subclass directly. Exposed creation methods for easier subclassing of SHKActionSheet. Discussed in #771