Fix auth renewal

[kulmann]

Fixes two things:

1. adds 401 error handling -> user will be presented with the authenticate button again. Trying to authenticate and then replay the previously failed requests is unfortunately a bigger task - won't happen in this PR (and also not planned effort short term). Did this by adding a) a response interceptor on the axios instance (used for graph API) and b) auth error handling in the catch block of the loadFolder method (webdav).
2. the filepicker initialization had a bug which made sense to solve here: if the user was initially authenticated the userLoaded event would always call updateBearerToken. If the user was initially unauthenticated the userLoaded event would always call initApp (which does a lot of things that are not needed on subsequent token renewals). Corrected the userLoaded event handler to call initApp if not in authorized state and then on subsequent token renewals call the updateBearerToken method instead.