Integrate Theme-Switch in translate5

we integrate a drop down that enables the user to switch himself between all available translate5 themes.

In the management area between help-button and language switch and in the editor as a sub menu in the view-mode drop-down below the language selection.

The text on the drop-down/the entry that leads to the sub-menu should be:

EN: Switch layout

DE: Layout wechseln

The dropdown/sub-menu entries should be the theme names that ExtJs offers.

translate5 should remember the theme a user selected.

The default theme of the application is the one configured in the system configuration.