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/MPInspectorViewController.m

@@ -139,6 +139,7 @@ typedef NS_ENUM(NSUInteger, MPContentTab) {
   self.observer = document;
   
   [self.entryViewController registerNotificationsForDocument:document];
+  [self.groupViewController registerNotificationsForDocument:document];
 }
 
 #pragma mark -