Add export process mode to frontend

requires backend!2470 (merged)

closes #1505 (closed)

Since for export processes the configuration view always is in read only mode (unless I misunderstood) this means that even if the process is not started you get the "process status" button: should I add a third option there

          <div class="column is-narrow">
            <button
              v-if="isConfigurable"
              class="button is-primary run"
              type="submit"
              :disabled="!canRun || processStarting || null"
              :title="runTitle"
            >
              Run process
            </button>
            <router-link
              v-else-if="isReadOnly"
              class="button is-success run"
              :to="{ name: 'process-details', id: process.id }"
              title="Got to process status page"
            >
              Process status
            </router-link>
          </div>

to have no button at all? Or do we not really care since export processes should not be "not started" unless something goes wrong + this doesn't actually do anything you just don't have anything except a warning on the process status page since it hasn't started