[TASK] Force "doktype" to be an integer in Menu ViewHelpers

This allows the use of ViewHelpers which fail on NULL values to use the "doktype" (which is zero for ordinary/unspecified pages).
[BUGFIX] When resolving shortcut data in MenuViewHelpers, fetch all fields of original page record
[BUGFIX] Page record incorrectly affected when resolving shortcut
[TASK] Remove argument "markdownExecutablePath" from MarkdownViewHelper

Constitutes a security risk if attacker gains access to templates. It should be noted that if an attacker can gain such access he can do far greater damage than just that - but anyway, this closes a potential hole.
[TASK] Adjust Exception message in Markdown ViewHelper