User manual: add visual resources

Polaris expressed that even with the user manual as a crutch, some of the more complex dialogues in the IBEX GUI can be a bit daunting.
As a Polaris instrument scientist, I would like the user manual to contain visual media to support the guides for common IBEX interactions, e.g. in the form of screenshots showing the interface at various steps, or video walkthroughs of common processes. Creating the latter may actually be less effort and provide more insight to the user.