refs #181

Until now the show context menu was only displayed when user’s were
visiting routes for that particular show. As we keep a global show
selection state, we can display this context menu at any time, because
the state is not unset when users visit other dashboard sites.

At least for now that makes sense.

This refactor includes a bulk of the changes discussed in #181. It
removes the existing navbar and replaces it with a sidebar instead. This
leaves us more room for context-aware navigation options and other
information that is relevant to users.

Additionally, the show management page is now split up into two, the
show episodes management, listing the coming shows/timeslots and the
show’s schedules, and the show basic data page, that contains all mostly
static data for a show and which is usually maintained by
administrators.

refs #181