Replace Preferences view. Removed LaunchAtLoginController and replaced with simpler code

ZeroTier One/PreferencesViewController.h

@@ -0,0 +1,21 @@
+//
+//  PreferencesViewController.h
+//  ZeroTier One
+//
+//  Created by Grant Limberg on 8/7/16.
+//  Copyright © 2016 ZeroTier, Inc. All rights reserved.
+//
+
+#import <Cocoa/Cocoa.h>
+
+@interface PreferencesViewController : NSViewController
+
+@property (nonatomic, weak) IBOutlet NSButton *startupCheckBox;
+
+- (IBAction)onStartupCheckBoxChanged:(NSButton*)sender;
+
+- (BOOL)isLaunchAtStartup;
+- (LSSharedFileListItemRef)itemRefInLoginItems;
+- (void)setLaunchAtLoginEnabled:(BOOL)enabled;
+
+@end