Remove need for third party url upload

- we can save the file to a variable, it requires a "url" returned
- we can get by returning an empty string

backend/src/schema/types/scalar/Upload.gql

@@ -1 +1 @@
-scalar Upload
+scalar Upload

webapp/components/ContributionForm/ContributionForm.spec.js

@@ -97,10 +97,9 @@ describe('ContributionForm.vue', () => {
       })
 
       describe('valid form submission', () => {
-        const imageUpload = {
-          file: { filename: 'avataar.svg', previewElement: '' },
-          url: 'someUrlToImage',
-        }
+        const imageUpload = [
+          { file: { filename: 'avataar.svg', previewElement: '' }, url: 'someUrlToImage' },
+        ]
         beforeEach(async () => {
           expectedParams = {
             mutation: PostMutations().CreatePost,
@@ -135,8 +134,8 @@ describe('ContributionForm.vue', () => {
         })
 
         it('supports adding a teaser image', async () => {
-          expectedParams.variables.imageUpload = imageUpload
-          wrapper.vm.vsuccess(imageUpload)
+          expectedParams.variables.imageUpload = imageUpload[0]
+          wrapper.vm.addTeaserImage(imageUpload)
           await wrapper.find('form').trigger('submit')
           expect(mocks.$apollo.mutate).toHaveBeenCalledWith(expect.objectContaining(expectedParams))
         })

webapp/components/ContributionForm/index.vue

@@ -8,7 +8,6 @@
           id="postdropzone"
           :use-custom-slot="true"
           @vdropzone-thumbnail="thumbnail"
-          @vdropzone-success="vsuccess"
           @vdropzone-error="verror"
         >
           <div class="dz-message">
@@ -108,7 +107,7 @@ export default {
       slug: null,
       users: [],
       dropzoneOptions: {
-        url: 'https://httpbin.org/post',
+        url: this.addTeaserImage,
         maxFilesize: 5.0,
         previewTemplate: this.template(),
       },
@@ -204,8 +203,9 @@ export default {
         this.form.languageOptions.push({ label: locale.name, value: locale.code })
       })
     },
-    vsuccess(file, response) {
-      this.form.teaserImage = file
+    addTeaserImage(file) {
+      this.form.teaserImage = file[0]
+      return ''
     },
     thumbnail: (file, dataUrl) => {
       let thumbnailElement, contributionImage, uploadArea