Revert "remove thumbnail cache"

This reverts commit e0db4931f1.

app/state/migrations.ts

@@ -1,26 +1,9 @@
-import { Store } from './store'
-import RNFS from 'react-native-fs'
-import { rmdir } from '@app/util/fs'
-
-const migrations: Array<(state: any) => Promise<any>> = [
-  async state => {
-    for (const server of state.settings.servers) {
+const migrations: Array<(state: any) => any> = [
+  state => {
+    for (let server of state.settings.servers) {
       server.usePlainPassword = false
     }
 
-    return state
-  },
-  async state => {
-    const store = state as Store
-    const keysToDelete = ['coverArtThumb', 'artistArtThumb']
-
-    for (const serverId in store.cacheDirs) {
-      for (const key in keysToDelete) {
-        await rmdir(`${RNFS.DocumentDirectoryPath}/servers/${serverId}/${key}`)
-        delete state.cacheFiles[serverId][key]
-      }
-    }
-
     return state
   },
 ]