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
If the mouse is over a TabItem and this TabItem is currently selected, then the color is not GrayhoverBrush, but HighlightBrush
ControlsHelper.HeaderFontSize is set to Inherited=true in order to allow to set the HeaderFontSize at TabControl level

<TabControl ControlsHelper.HeaderFontSize="20">
....
Revert "special property" behavior
Revert space missmatch
If isEditable is enabled Background is not properly set
Merge pull request #1575 from CoryMcDonald/master

If isEditable is enabled Background is not properly set
Merge pull request #1547 from xxMUROxx/hotfix/TabItem

[Fix] TabControl, MouseOver & IsSelected Background color
Merge pull request #1510 from Dotnetifier/floating-watermark

Added the Floating Watermark feature
Use .First instead of .Single, so we don't iterate over the list 5 billion times
Merge remote-tracking branch 'upstream/master'