Update FlatSlider.xaml

User can define width of vertical slider / height of horizontal slider
Update Icons.xaml

Added the following icons:
appbar_bold
appbar_italic
appbar_underline
appbar_font
appbar_fontsize
appbar_fontsize_increase
appbar_fontsize_decrease
appbar_textcolor
appbar_marker
Update TransitioningContentControl.cs
Update MainWindow.xaml
Update MainWindow.xaml.cs
Update GlowWindow.xaml.cs

Fixes the cursor when owner.ResizeMode is ResizeMode.NoResize or ResizeMode.CanMinimize.
Merge remote-tracking branch 'MetroBehind/master'
Changed watermark margin to same settings as in textboxes
Tab showing accent brushes
Fix some tests
Reproduce #990
Minor cleanups
Simplify the WindowCommands handling for the clean window style

We introduce the property "OverrideDefaultWindowCommandsBrush" that is
default by null.
CleanWindowStyle ovverides this to "BlackBrush"

This fixes #990
Update release notes
Merge pull request #991 from MahApps/fix-990

Simplify the WindowCommands handling for the clean window style
Update NuGet
Fix the build

Fixes #995
publish 0.12.1
fixing external dialogs (fixes #994)
naming