Restructure Documentation layout

[kprosise]

The documentation for docs.mion.io should be organized to make it both easier to navigate and easier to maintain.

Technical documentation is tied to releases, but other information such as community topics is not. Rather than having versioning applied to all documentation, it is sensible to only have it apply to technical documentation.

Within mion-docs, parent-child relations should be implemented, and grouped together in directories.

[kprosise]

This has been done to a very minor extent, however as many pages will be eventually moved to the NGL site, the current layout is good enough until that point.