Imessageservice and behavior fixes WIN81WPRT81

WIN81 & WPRT81 fix for ImessageService and Behavior for PasswordBox
updated Behavior to support more control

as suggested by Geert
Enabled UseLayoutRounding on default styles
Merge pull request #19 from SinghsX/develop

IMessageService for WIN81 and WPRT81, fixed Behavior.cs bug.
Moved several files to NET40 in preparation to an eventual shared project refactoring
Added several behaviors to WP 8.1 RT
(x) CTL-429 Several code improvements for StyleHelper