Various fixes and improvements (#1643)

- allow repo names to be case-insensitive
- improve backend error handling on DB get errors (record not found ->
404, else -> 500)
- replace magic numbers of http response codes
- unify the look and feel of cancel / save buttons on forms and view
them in one line

---------

Co-authored-by: Lauris BH <lauris@nix.lv>

web/src/components/admin/settings/AdminUsersTab.vue

@@ -27,7 +27,8 @@
         <IconButton
           icon="edit"
           :title="$t('admin.settings.users.edit_user')"
-          class="ml-2 w-8 h-8"
+          class="w-8 h-8"
+          :class="{ 'ml-auto': !user.admin, 'ml-2': user.admin }"
           @click="editUser(user)"
         />
         <IconButton