Stubbed custom attribute adding via context menu

Made MPContextToolbarButton usable as normal button.
Added private API helper for adding buttons to NSUserNotification
Remove Autotype plugin API
Enhanced custom attribute plugin API
Enhanced EntryActionPlugin API to decouple menu items from actual action/target setup
Stubbed action on no-open documents NSUserNotifications
Stubbed HMACOTP custom attribute setup

MacPass/MPAddCustomFieldContextMenuDelegate.m

@@ -0,0 +1,58 @@
+//
+//  MPAddCustomFieldContextMenuDelegate.m
+//  MacPass
+//
+//  Created by Michael Starke on 05.12.17.
+//  Copyright © 2017 HicknHack Software GmbH. All rights reserved.
+//
+
+#import "MPAddCustomFieldContextMenuDelegate.h"
+#import "KeePassKit/KeePassKit.h"
+
+NSString *const MPHMACOTPSeedAttributeKey = @"HMACOTP-Seed";
+NSString *const MPHMACOTPConfigAttributeKey = @"HMACOTP-Config";
+
+@interface MPAddCustomFieldContextMenuDelegate ()
+@property (readonly, nonatomic) KPKEntry *entry;
+@end
+
+@implementation MPAddCustomFieldContextMenuDelegate
+
+- (KPKEntry *)entry {
+  KPKEntry *entry = self.viewController.representedObject;
+  if([entry isKindOfClass:KPKEntry.class]) {
+    return entry;
+  }
+  return nil;
+}
+
+- (void)menuNeedsUpdate:(NSMenu *)menu {
+  [menu removeAllItems];
+  [self _setupHOTPMenuItemsToMenu:menu];
+}
+
+- (void)_setupHOTPMenuItemsToMenu:(NSMenu *)menu {
+  
+  BOOL hasConfigAttribute = nil != [self.entry customAttributeWithKey:MPHMACOTPConfigAttributeKey];
+  if(!hasConfigAttribute) {
+    NSMenuItem *item = [[NSMenuItem alloc] initWithTitle:@"Add config" action:@selector(_addHMACConfig:) keyEquivalent:@""];
+    item.target = self;
+    [menu addItem:item];
+  }
+  BOOL hasSeedAttribute = nil != [self.entry customAttributeWithKey:MPHMACOTPSeedAttributeKey];
+  if(!hasSeedAttribute) {
+    NSMenuItem *item = [[NSMenuItem alloc] initWithTitle:@"Add seed" action:@selector(_addHMACSeed:) keyEquivalent:@""];
+    item.target = self;
+    [menu addItem:item];
+  }
+}
+
+- (IBAction)_addHMACConfig:(id)sender {
+  [self.entry addCustomAttribute:[[KPKAttribute alloc] initWithKey:MPHMACOTPConfigAttributeKey value:@"<config>"]];
+}
+
+- (IBAction)_addHMACSeed:(id)sender {
+  [self.entry addCustomAttribute:[[KPKAttribute alloc] initWithKey:MPHMACOTPSeedAttributeKey value:@"<seed>"]];
+}
+
+@end