Up until now the application was crammed in a single JavaScript file
once bundled. This forces clients to download 1.1MiB of JavaScript all
at once.

Vite uses dynamic import statements as split-points for bundles. By
using dynamic imports for our routes we can delay the loading of some
data to a later point in time when the user actually needs it. We should
still try to reduce our overall bundle size.

Notable changes:
 * Vue 2.6 to Vue 3 + compat migration.
 * Build system migration from vue-cli/webpack to Vite.
 * Application dependencies like bootstrap-vue, vue-router, vuex,
   or vue-toast-nofitication have been updated, if doing so was
   necessary or advisable for the Vue 3 migration.
 * Static file includes for the oidc-client in oidc_callback.html
   and oidc_callback_silentRenew.html have been removed in favor
   of automatic processing in the build system so that all assets
   are versioned and invalid cache hits are prevented.

Fixes #53 and #110.