Fix Mv.dual() default mode to use I-inverse

[utiberious]

Mirrors issue 514 from upstream. The default dual mode 'I+' computes selfI which gives wrong results. The conventional Hodge dual uses selfI^{-1}. Changed default to 'Iinv+' so that B*dual(B)=I holds.

[utiberious]

Branch pushed: https://github.com/utiberious/galgebra/tree/fix/issue-514-mv-dual

Fixed Mv.dual() default mode to use I-inverse (right multiplication by pseudoscalar inverse) instead of just I, which is the conventional definition. Includes test.