SideBySide2: Hide CodeMirror when dialogs display

If ErrorDialog shows while CodeMirror is visible many of the
CodeMirror elements show above the dialog.  CM3 uses a number
of z-index values to display its content and some of them are
higher than the GWT dialogs.

Use a global handler registration system to hide CM3 widgets
when a dialog opens, similar to how flash movies are hidden.

Set the z-index of SearchPanel's popup and UserInfoPopup to 5
to make sure it's on top of all CodeMirror widgets.

Change-Id: Ied80d0ec8deeab574c9d661aabbbe26eeb70e74a
9 files changed