Release 4.4.0

• Merge remote-tracking branch 'origin/master' (bee8ad1)
• Merge pull request #559 from firepixy/improved-avatar-by-firepixy (8863bfb)
• fix(lib): updated firebase (0b47932)
• NgxAuthFirebaseuiAvatarComponent: button with CSS class (a575a2a)
• Demo: updated example for ngx-auth-firebaseui-avatar (866b669)
• Docs: updated ngx-auth-firebaseui-avatar.md (0784050)
• NgxAuthFirebaseuiAvatarComponent: new input properties (b61b7c9)
• fix(lib): updated the dependeicies (91b75d3)
• fix(lib): apple provider is set ti lower case #397 (18701ca)
• Merge pull request #556 from semla/master (fbeff35)
• auth.component: Make Go back button optional (f3c0d79)