Fix Font.FromName to work with spaces in font names

It will now split on the last space to get the size
[Gtk] Protect against a null reference exception

Sometimes ImplicitMinSize is called when the Child is null which
causes a null reference exception. I don't know exactly what triggers
it as it's quite rare.
[Mac] Rewrite to use CoreGraphics for Context and CoreText for TextLayout

The CGContext API is very similar to Cairo, enables us to set the global alpha,
and is probably more performant than calling the Objective-C drawing routines in AppKit.
Also use CoreText for TextLayout because it works with a CGContext and enables us to wrap
text correctly based on the given width.

Basically, the Mac drawing samples look much more like the Gtk version now.
Add Xwt.Drawing.Path API with Gtk, WPF, and Mac implementations and a sample

This causes Context to now extend from a new Path class, which contains
all the drawing path methods (Arc, Rectangle, CurveTo, etc.) and adds new
hit testing methods.
[GTK] Fix drawing issue in Canvas
Merge branch 'master' into multi-toolkit-lluis

Conflicts:
	Xwt.Gtk/Xwt.CairoBackend/CairoContextBackendHandler.cs
	Xwt.Gtk/Xwt.GtkBackend/GtkEngine.cs
	Xwt.Mac/Xwt.Mac.csproj
	Xwt.Mac/Xwt.Mac/CanvasBackend.cs
	Xwt.Mac/Xwt.Mac/ContextBackendHandler.cs
	Xwt.Mac/Xwt.Mac/MacEngine.cs
	Xwt.Mac/Xwt.Mac/TextLayoutBackendHandler.cs
	Xwt/Xwt.Backends/IContextBackendHandler.cs
	Xwt/Xwt.Drawing/Context.cs
	Xwt/Xwt.Drawing/Font.cs
	Xwt/Xwt.csproj
Track api changes
Revert "Add Xwt.Drawing.Path API with Gtk, WPF, and Mac implementations and a sample"

Keep master stable and have this in a branch for now.
This reverts commit 2e2f04610e3667c214ffd32bfc8eb0b04333057c.
Merge branch 'master' into xwt-next

Conflicts:
	Xwt.Gtk/Xwt.CairoBackend/CairoContextBackendHandler.cs
	Xwt.Gtk/Xwt.GtkBackend/GtkEngine.cs
	Xwt.Mac/Xwt.Mac.csproj
	Xwt.Mac/Xwt.Mac/ContextBackendHandler.cs
	Xwt.Mac/Xwt.Mac/MacEngine.cs
	Xwt.Mac/Xwt.Mac/PathBackendHandler.cs
	Xwt/Xwt.Backends/IContextBackendHandler.cs
	Xwt/Xwt.Backends/PathBackendHandler.cs
	Xwt/Xwt.Drawing/Context.cs
	Xwt/Xwt.Drawing/Path.cs
	Xwt/Xwt.csproj
Rename Path to DrawingPath to eliminate any possible name conflicts with System.IO.Path
Track api changes in WPF backend
Fix color parsing
Fix widget layout issue

Don't reallocate widgets which don't yet
have a parent. Added method for determining
if a widget has a native parent.
[WPF] Fix reallocation issue

Reallocate the root widget when a window is rearranged.
[WPF] Fix window size calculation bug

In WPF, the size of the client area depends on the size of the window borders,
and the border size changes if the window is resizable or fixed. Now we
use the correct border size depending on the size mode. Also, we now ensure
the size of the client area doesn't change when the size mode changes.
[WPF] Don't include the margin when calculating the size of a widget
[WPF] Fix window padding bug
[API] Remove ResetTransform from Drawing API and update Backends, Samples, etc

ResetTransform cannot be safely implemented in Mac CoreGraphics.
The same functionality is available using a Save/Restore pair, so it can be removed.
An unfortunate case of the Backend wagging the API!
Merge pull request #135 from hwthomas/master

[API] Remove ResetTransform from Drawing API
Improvements in application initialization

When initializing XWT, the backend can now be
specified using an enumeration. 

XWT now loads backends which match the version
number of Xwt.dll.