Various usability improvements (#665)

* Set password creator window title

* Fix TODO, help url is read from Info.plist instead of a string literal

* Remove width constraint for 'Set Defaults' button of password generator so text is not cropped

* Improve keyboard shortcuts
New entries can be created using cmd + n, while cmd + shift + n creates new groups. Creating new databases is probably done too rarely to warrant a keyboard shortcut.
Additionally the 'New' menu item now has a submenu containing actions to create new entries, groups and databases (fixing #405).

* Hook up keyboard shortcut cmd + backspace to delete action

* Use shorter date format in inspector and add special output for distant future

* Show date picker when expiration is activates for either groups or entries but no date set

* Prompt for key file pops up automatically when the field is selected using tab

* Focus title field when new groups are created (#606).

* Rename search method so text fields don't capture it (#531)

* Don't show empty tags

* Remove menu item used for debugging.

MacPass/MPPathControl.h

@@ -0,0 +1,16 @@
+//
+//  MPPathControl.h
+//  MacPass
+//
+//  Created by Christoph Leimbrock on 8/7/17.
+//
+
+#import <Cocoa/Cocoa.h>
+
+@protocol MPPathControlDelegate <NSPathControlDelegate>
+- (void)pathControlDidBecomeKey:(NSPathControl *_Nullable)control;
+@end
+
+@interface MPPathControl : NSPathControl
+@property (nullable, weak) id <MPPathControlDelegate> delegate;
+@end