Allow to have search popup sticky

[ystrot]

Moved from http://code.google.com/p/eclipse-glance/issues/detail?id=11

The standard Ctrl-F search is a non-modal window, so you can still search,
type and scroll trough the window while having a search window on top. It
would be great if glance search popup worked similarly. That would help
with navigating to highlighted text appearances using markers on right
Editor navigation bar.

[ystrot]

I think we can do this one using SWT.ON_TOP instead of modal dialog. Modal dialogs are evil, that's right :-)