[che-dev] Changelog: CHE-676

[4_0-changeslog@xxxxxxxxxxx]

[che-dev] Changelog: CHE-676
1. Keep focus on dialog when user uses tab button
2. Change behavior for focus() of org.eclipse.che.ide.ui.window.Window: <https://github.com/eclipse/che/blob/master/core/ide/che-core-ide-ui/src/main/java/org/eclipse/che/ide/ui/window/Window.java#L190> 
Now it set focus on last focused element if such exist: <https://github.com/eclipse/che/blob/master/core/ide/che-core-ide-ui/src/main/java/org/eclipse/che/ide/ui/window/View.java#L298> 
But if you display dialog, last focused elemet = null, so it's impossible to set focus in this use case. After my changes it will set focus on the first child of content panel if such exists. Otherwise it will set focus on first child of footer
<https://github.com/eclipse/che/pull/611>