Enable keyboard shortcuts

Feature

• Keyboard shortcuts should be available for some major actions as e.g. for selecting views.
• Not all operations are reachable by keyboard shortcuts, e.g. if multiple objects such as job chains are displayed on screen
• A specification is required that explains which actions should be supported by keyboard shortcuts

Maintainer Note

• This featue is dismissed as there is no chance for a satisfactory functionality: most views show a number of items for which operations are available, e.g. list of job chains, jobs, history entries etc. that would be hard to select by keyboard.
• In fact the switch of views could be enabled by keyboard shortcuts, however, the functionality would remain incomplete concerning the handling of lists as the user would always have to use a mouse/touchpad/touchscreen etc.