Added the Floating Watermark feature
Some editions to the floating watermak

Changed the whole storyboards.
Moved the storyboards to Shared.xaml, to share them in both TextBox.xaml
and PasswordBox.xaml.
Edited TextBoxes with buttons too
Merge pull request #1 from mrahhal/mrahhal-floating-watermark

Some editions to the floating watermak
Added FloatingWatermark in MetroDemo
Floating watermark font size in Fonts.xaml
Merge pull request #1510 from Dotnetifier/floating-watermark

Added the Floating Watermark feature