Overview improvements

Contains several improvements and fixes to the overview page:

• Added new "NoData" component so that the same layout can be retained even if some data is missing.
• Fixed issues with trying to access missing SCCS, methods, or systems
• Added direct communication between plots/structures through RxJS Subjects. After researching what other people have done in a similar situation, this approach popped up in multiple locations. Essentially it is just the PubSub pattern. Bypassing the rendering with this approach seems to give a nice performance boost to Plot interactivity. @mscheidg: I think this is quite a clean and versatile approach, but if you can suggest any improvements they are certainly welcome.
• Modified the ToggleButton text opacity a bit so that it does not look like it is disabled.
• Improved the initial translation/orientation of structures shown by the Structure component so that systems have a more "natural" initial state in the overview page.
• Changed the order of Material and API access buttons.

Before merging I would suggest that you check and modify the NoData component visuals to your liking.