[issue #4] initial empty routing

Created all new files that reflect the routing of the application, they
are empty. Also introduced initialiser files that shall be used to
mananage the different dependencies of the modules.
[issue #4] initial navbar

Create the initial navbar, however, still very ugly and does not contain
the tree and selection context stuff.
[issue #4] initial rudimentary exercise nav

Add initial rudimentary exercise nav that slides in and out if it is
actually needed. The nav component content is not present at all.