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

src/plugins/nativestorage.ts

@@ -33,6 +33,7 @@ export class NativeStorage {
    * Stores a value
    * @param reference {string}
    * @param value
+   * @returns {Promise<any>}
    */
   @Cordova()
   static setItem(reference: string, value: any): Promise<any> {return; }
@@ -40,6 +41,7 @@ export class NativeStorage {
   /**
    * Gets a stored item
    * @param reference {string}
+   * @returns {Promise<any>}
    */
   @Cordova()
   static getItem(reference: string): Promise<any> {return; }
@@ -47,12 +49,14 @@ export class NativeStorage {
   /**
    * Removes a single stored item
    * @param reference {string}
+   * @returns {Promise<any>}
    */
   @Cordova()
   static remove(reference: string): Promise<any> {return; }
 
   /**
    * Removes all stored values.
+   * @returns {Promise<any>}
    */
   @Cordova()
   static clear(): Promise<any> {return; }