Fix some warnings regarding protocols and missing implementation

Sources/VLCCloudStorageController.m

@@ -10,4 +10,20 @@
 
 @implementation VLCCloudStorageController
 
++ (VLCCloudStorageController *)sharedInstance {
+    return nil;
+}
+- (void)startSession
+{
+    // nop
+}
+- (void)logout
+{
+    // nop
+}
+- (void)requestDirectoryListingAtPath:(NSString *)path
+{
+    // nop
+}
+
 @end

Sources/VLCCloudStorageTableViewController.h

@@ -15,7 +15,7 @@
 #import "VLCCloudStorageTableViewCell.h"
 #import "VLCCloudStorageController.h"
 
-@interface VLCCloudStorageTableViewController : UIViewController
+@interface VLCCloudStorageTableViewController : UIViewController <VLCCloudStorageDelegate>
 
 @property (nonatomic, strong) IBOutlet UITableView *tableView;
 @property (nonatomic, strong) IBOutlet UIView *loginToCloudStorageView;

Sources/VLCCloudStorageTableViewController.m

@@ -15,7 +15,7 @@
 #import "VLCCloudStorageTableViewController.h"
 #import "VLCProgressView.h"
 
-@interface VLCCloudStorageTableViewController() <VLCCloudStorageDelegate>
+@interface VLCCloudStorageTableViewController()
 {
     VLCProgressView *_progressView;
     

Sources/VLCPlaybackController.h

@@ -17,6 +17,7 @@
 
 @protocol VLCPlaybackControllerDelegate <NSObject>
 
+@optional
 - (void)playbackPositionUpdated:(VLCPlaybackController *)controller;
 - (void)playbackRateUpdated:(float)rate forPlaybackController:(VLCPlaybackController *)controller;
 - (void)mediaPlayerStateChanged:(VLCMediaPlayerState)currentState