Find: Use greedy behaviour

Find: Use greedy behaviour

This change is valid for findadv too.
Patterns like '.*' now are greedy, like it is normal in regex
Searching for whole words is corrected, but can be slow.
One can speed up the search with adapted pattern.
So for instance searching for words starting and ending with 'r'
the normal pattern is 'r.*r'. The speed-up pattern could be
'\br[^\s]*r\b'. This halves the search time.

Search results are now different to that of lyx2.3, because the greedy
'.*' is now really greedy.
To achive the same results, we have to use '.*?' instead.