Improve wizzard to mount devices or platforms

As a user I want to be the process to mount devices or platforms somehow easier, as the current state of the tree usage (I have to click on the platform to mount things on it) is not intuitive. Instead I want to have a wizzard instead so that I can focus on one step at a time.

Tobias already started by building this kind of wizzrd. It is currently also in the develop branch.

The current wizzard has the following stages:

• selection of the date for the mount
• selection of the parent platform
• search for devices & inserting the data (offsets, description of the mount, contact)
• overview with submit button

We want to improve this in the further things:

• instead of the text Choose node we want to have Choose parent platform as those are the only option (no parent devices are possible for the moment)
• the search & insert step should be splitted into search alone (+ checkboxes to select devices/platforms for the next state) and then a step where the data (offsets, ...) can be inserted for the selected devices/platforms
• devices/platforms selected for the mount should be clearly visible (checkboxes or highlighting or ...)
• the overview page with the submit should have the option to get back to the edit of the mount data
• the overview page should have the option to jump back to a step so that we can deselect a platform or devices that was selected before (but we decided that we don't want to mount that before the submit)
• the submit page itself should just stay as an overview (no direct editing here)
• the user must either set the mount to unlimited or should insert an end date
• we want to extract the platform mount end dates, so that we can enforce an end date for the new mounts that is before the platform unmount (and of cause show it to the user)
• we want to ask the backend about the availabilty information, so that we can show that the devices / platforms are either not available at all or only up to a certain point in time
• we want to validate that those end dates are respected in the user input
• we want to add hints so that it is clear that the offsets are relative to the parent platform (or the root if no parent platform)
• in the tree for the parent platform selected the devices should be disabled (ausgegraut), so that is clear that only platforms can be selected
• it should be possible to select both platforms & devices to mount in one batch (for the very same parent paltform & start date)
• of cause: Usage of the vuex store

Nice to have:

• we want to show the configuration tree as live-preview, so that the user knows where she/he is going to insert which devices
• display computed offsets to the root if parent platform is selected
• mechanism to copy the end date of another mount in the same batch (say I want to mount 7 devices & know already that I will unmount all of them on the same time) (low priority)

Important: For all that we decide not to do in the nice-to-have section: Please add extra issues then so that we can care about the functionality later!!