Ability to preview and upload logo and background images

Re: pleroma#1516 (closed)

Complementary BE MR pleroma!2388 (merged)

Screenshots:

mobile

src/api/mediaUpload.js

-import { getToken, getAuthHost } from '@/utils/auth'
+import { getToken } from '@/utils/auth'
 import { baseName } from './utils'
 
-const UPLOAD_URL = '/api/pleroma/admin/upload_media'
+const UPLOAD_URL = '/api/v1/media'
 
-export function uploadMedia({ formData }) {
-  const url = baseName(getAuthHost()) + UPLOAD_URL
+export function uploadMedia({ formData, authHost }) {
+  const url = baseName(authHost) + UPLOAD_URL
 
   return fetch(url, {
     body: formData,