Fixed #192: Dynamically adjust the suggestion list in the new UI.
Use the same window flags for the scan window, on Win and Linux.

Previously, the scan popup used Qt::Popup flag on Linux, but this
flag is incompatible with the new translate box UI, esp. the
floating suggestion list, since in the Qt::Popup-styled windows
all the events go to the popup, hence the creation of additional
windows is problematic, and those new windows don't work properly
since they don't receive events.

Without this change, the scrolling of the suggestion list in the
Scan Popup's translate box is impossible.
Properly hide the suggestions list in some cases.
Revert "Use the same window flags for the scan window, on Win and Linux."

Unfortunately, the change didn't work properly on KDE systems.

This reverts commit 8a8c7cc7d7356495bf3ae53c0f01a266143e49ee.
Make the suggestion list to be internal instead of top-level window, on *nix.

This should solve the conflict between the Qt::Popup-styled Scan window and
the suggestion list.

Tested on Windows 7, Lubuntu (XFCE) and Mint (KDE).