Support self:: in static trait methods accessed from outside

[roberthusak]

This issue is related to #135, aimed at the usage of self:: in such situations. Test case:

<?php
trait T {
  private static $bar = "right";
  public static function bar() {
    return self::$bar;
  }
}
class C {
  public static $bar = "wrong";
  public static function foo() {
    return T::bar();
  }
}
echo C::foo();
echo "\n";
echo T::bar();

Expected result:

right
right

Actual result:

wrong

Unhandled Exception: System.NotImplementedException: The method or operation is not implemented.
   at Pchp.Core.Dynamic.GetFieldBinder.Bind(DynamicMetaObject target, DynamicMetaObject[] args)
   at System.Dynamic.DynamicMetaObjectBinder.Bind(Object[] args, ReadOnlyCollection`1 parameters, LabelTarget returnLabel)
   ...

Also, Debug.Assert(ReferenceEquals(newOwner.OriginalDefinition, this.ContainingSymbol.OriginalDefinition)) in FieldSymbol.AsMember fails during the compilation.