Also some less significant improvements.

Reviewed-by: Robert Loehning

Hierarchy information removed from tooltips now.

To catch cases of invalid code like this:
struct A : B {};
struct B : A {};

Reviewed-by: Roberto Raggi

The old integration option is now used to switch to extended descriptions.

We need to add the fully qualified name to the case statements.

Reviewed-by: Roberto Raggi

To conform with recent changes that affected LookupContext::fullyQualifiedName.

Task-number: QTCREATORBUG-1169

Also removed TokenUnderCursor as it's functionality is in the token cache.

Reviewed-by: ckamm

 - lessens open file handles
 - improves help plugin startup further

Task-number: QTCREATORBUG-337
Reviewed-by: ck

This reverts commit c2393df0.

This should speed things up a bit, because before, the line was tokenized at
least 3 times.

Was broken in 915a07bd, which caused
help links only to be resolved for expressions under the cursor.

Task-number: QTCREATORBUG-159
Reviewed-by: ckamm

Since the fix in 01a0ec16, sometimes
& would turn up in the tooltips due to them being escaped but not
interpreted as HTML.

Turns out the <nobr> actually caused wrapping in some cases because the
tag made the QToolTip turn on its wrapping feature due to the text being
rich text. So avoid adding it to plain text tooltips unnecessarily.

Reviewed-by: hunger
Task-number: QTCREATORBUG-1169

If the generated documentation doesn't contain the namespace name,
we failed to look up the correct help page.

Task-number: QTCREATORBUG-946
Reviewed-by: Erik Verbruggen

Reviewed-by: Thorbjørn