Fixed incorrect behaviour of Natural button in Surface Inspector

Code in TextureProjection::constructDefault moved into actual default
constructor. This obtains the default texture scale from the registry. Removed
the static TextureProjection::Default() instance since we need to
default-construct new TextureProjection objects in order to get the updated
scale.
Removed unused members

m_basis_s and m_basis_t were set and copied but never used in any calculation.