rework SymbolFactory

- rename & move to Pilz.UI..Telerik.Symbols.RadSymbolFactory
- make default implementaiton available at Pilz.UI.Symbols.SymbolFactory
- add interfaces

Pilz.Plugins.Advanced.UI.Telerik/Pilz.Plugins.Advanced.UI.Telerik.csproj

@@ -9,7 +9,6 @@
 
   <ItemGroup>
     <ProjectReference Include="..\Pilz.Plugins.Advanced.UI\Pilz.Plugins.Advanced.UI.csproj" />
-    <ProjectReference Include="..\Pilz.UI.Telerik.SymbolFactory\Pilz.UI.Telerik.SymbolFactory.csproj" />
     <ProjectReference Include="..\Pilz.UI.Telerik\Pilz.UI.Telerik.csproj" />
   </ItemGroup>