AssetAdmin: PHP warning trying to add empty values into CompositeField

If the logged in user doesn't have permission to add a Folder record,
AssetAdmin::getEditForm() tries to enter an empty value into the
children of a ComposteField. This breaks SSViewer with a
call_user_func invalid args PHP warning.

Only include these buttons when they're available to the user.
Merge pull request #840 from halkyon/compositefield_assetadmin_warning

AssetAdmin: PHP warning trying to add empty values into CompositeField
Updated translations
Hints for SiteTree.TreeTitle casting

Relates to SS-2013-009
Clearer escaping in ReportAdmin

No direct security issue since report titles can't be set by the user
FIX Escaping in "dependent pages" (SS-2013-009)
Clearer escaping in CMSMain

No direct security issue, but makes intent clearer