XFCE Optional Xfce4 Session and Startup Settings

[Elfy]

Various fixes required prior to testing 14.10

Testcase 1576:

(This test will check that Session chooser appears at login. Logging out will be required.)
From Action buttons choose logout, select Save session for future logins should be
From whiskermenu power button choose logout, select Save session for future logins in logout dialogue

(This test will check that applications are restored with sessions. Logging out will be required.)
From Action buttons choose logout should be
From whiskermenu power button choose logout

(This test will check that Session saves are cleared correctly. Logging out will be required.)
From Action buttons choose logout should be
From whiskermenu power button choose logout