I10N: First translation fixes for 2.1

Fix README, some spelling errors, remove contractions,
exclamation marks, correct some plural forms, join split messages.
Add QCoreApplication::translate to non-Q_OBJECT-classes.
Fix some lupdate warnings about discarding meta-data (//:).

src/plugins/debugger/stackhandler.cpp

@@ -130,7 +130,6 @@ QVariant StackHandler::data(const QModelIndex &index, int role) const
     if (role == StackFrameAddressRole)
         return frame.address;
 
-    //: Tooltip for variable
     if (role == Qt::ToolTipRole)
         return frame.toToolTip();