Code refactoring to implement suggestions from the code review.

Binding the touchIdEnabled Buttons state directly to the userdefaults
value.

Fixed bug that disabled the TouchIdEnabled button on an unsucessfull
TouchId unlock

MacPass/MPPasswordInputController.m

@@ -29,6 +29,7 @@
 #import "MPTouchBarButtonCreator.h"
 #import "MPSettingsHelper.h"
 #import "MPConstants.h"
+#import "MPSettingsHelper.h"
 
 #import "HNHUi/HNHUi.h"
 
@@ -90,10 +91,11 @@ - (void)viewDidLoad {
   [self.enablePasswordCheckBox bind:NSValueBinding toObject:self withKeyPath:NSStringFromSelector(@selector(enablePassword)) options:nil];
   [self.togglePasswordButton bind:NSEnabledBinding toObject:self withKeyPath:NSStringFromSelector(@selector(enablePassword)) options:nil];
   [self.passwordTextField bind:NSEnabledBinding toObject:self withKeyPath:NSStringFromSelector(@selector(enablePassword)) options:nil];
+  NSUserDefaultsController *defaultsController = [NSUserDefaultsController sharedUserDefaultsController];
+  [self.touchIdEnabledButton bind:NSValueBinding toObject:defaultsController withKeyPath:[MPSettingsHelper defaultControllerPathForKey:kMPSettingsKeyEntryTouchIdEnabled] options:nil];
   self.touchIdEnabledButton.hidden = true;
   if (@available(macOS 10.13.4, *)) {
     self.touchIdEnabledButton.hidden = false;
-    self.touchIdEnabledButton.state = [NSUserDefaults.standardUserDefaults integerForKey:kMPSettingsKeyEntryTouchIdEnabled];
     [self _touchIdUpdateToolTip];
   }
   [self _reset];
@@ -371,12 +373,11 @@ - (IBAction)unlockWithTouchID:(id)sender {
   if(success) {
     return;
   }
-  [self.touchIdEnabledButton setEnabled:false];
+  [self.touchIdButton setEnabled:false];
   [self _showError:error];
 }
 
 - (IBAction)touchIdEnabledChanged:(id)sender {
-  [NSUserDefaults.standardUserDefaults setInteger: self.touchIdEnabledButton.state forKey:kMPSettingsKeyEntryTouchIdEnabled];
   [self _touchIdUpdateToolTip];
 }