scide: fix whitespace
scide: Document: merge the two constructors
scide: process Document-related SC messages in DocumentManager
scide: DocumentManager: keep sensitive information private
scide: DocumentManager: improve QString and QByteArray handling

* Use implicit construction via const char* where appropriate
* Treat as UTF-8 encoded bytes where appropriate
scide: fix "aScIDEDocument.front"

* Do not scroll to top of document and deselect
* Delete unused DocumentManager::showDocument()