#1352 Default the Extended Search to "All Docs"

[Dellu]

Defaulting for Current Doc doesn't make sense because if the user wants to search just in the current Doc, she doesn't need to call for the Extended Search. She can just use the simple/standard search window.

I am suggesting "All Docs" because many of use do not use Projects.
As I have suggested before, it would also be nicer if the selected choice (Project or All Docs) would be sticky (same when Texstudio is restarted).