docs(all): standardizes and adds return types, also some param fixes

src/plugins/imagepicker.ts

@@ -55,7 +55,7 @@ export class ImagePicker {
   /**
    * Pick pictures from the library.
    * @param {ImagePickerOptions} options
-   * @return Returns a Promise that resolves the image file URI
+   * @returns {Promise<any>} Returns a Promise that resolves the image file URI
    * otherwise rejects with an error.
    */
   @Cordova({