BaseSchemaTree: new constructor

Takes a BaseSchemaTree and a new JsonPointer as an argument.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
Simplify BaseSchemaTree and derivates a lot

For one, in InlineSchemaTree, we don't recalculate the refs anymore.

And all private constructors now call upon super().

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>