Kexi: Added minimal global search implementation with autocompletion

MainWindow
*Added minimal global search implementation with completion list, now just searches within Project objects
**after pressing Enter - select object name in Project Navigator
**on highlighting in completion list, highlights the object name
**[code]QCompleter which cannot do substring matching (https://bugreports.qt.nokia.com/browse/QTBUG-3414)
**[code]KCompletion is not better
**[code]Forked QCompleter and related classes and put in KexiUtils

DIGEST: Kexi: Added minimal global search implementation with autocompletion