Help: Avoid trying to open "Foo::bar" as a url in a browser.

Technically it is a valid URL with scheme "Foo" and path ":bar". With
this patch we only try to open URLs with very specific schemes like
"qthelp", "file", "http(s)", "about".

Task-number: QTCREATORBUG-7547
Change-Id: I6908ff554c12ca0f4cfc5bd0fb30dd659d780a23
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>
Help: Fix finding latest Qt documentation link for Qt5

The identifiers changed to use org.qt-project.
Also simplify the logic the does the id highlighting.

Task-number: QTCREATORBUG-10331
Change-Id: I3b6eb80138d8fafeb84772b95435acd68818ada1
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>