Add MediaService

This service is responsible for operations regarding uploaded media. It should perform save, get and delete operations with the configured backend.
The service also checks, if the mime type of the uploaded media is allowed.

Signed-off-by: David Mehren <git@herrmehren.de>

src/media/multer-file.interface.ts

@@ -0,0 +1,32 @@
+import { Readable } from 'stream';
+
+// Type from https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/multer/index.d.ts
+export interface MulterFile {
+  /** Name of the form field associated with this file. */
+  fieldname: string;
+  /** Name of the file on the uploader's computer. */
+  originalname: string;
+  /**
+   * Value of the `Content-Transfer-Encoding` header for this file.
+   * @deprecated since July 2015
+   * @see RFC 7578, Section 4.7
+   */
+  encoding: string;
+  /** Value of the `Content-Type` header for this file. */
+  mimetype: string;
+  /** Size of the file in bytes. */
+  size: number;
+  /**
+   * A readable stream of this file. Only available to the `_handleFile`
+   * callback for custom `StorageEngine`s.
+   */
+  stream: Readable;
+  /** `DiskStorage` only: Directory to which this file has been uploaded. */
+  destination: string;
+  /** `DiskStorage` only: Name of this file within `destination`. */
+  filename: string;
+  /** `DiskStorage` only: Full path to the uploaded file. */
+  path: string;
+  /** `MemoryStorage` only: A Buffer containing the entire file. */
+  buffer: Buffer;
+}