revert binop, add and use as_quantity(), fix uncertainties
add subsref to ureg to index aliases

* move times() in unit up with other overriden methods
* add combine() to unit to combine bases
* remove DOF property
fix bugs in `Quantities.unit.combine()`

* update legacy quantity _unit_ property to `units` now, 3 found in
 `unit.times()`
* add if degree==0 then don't combine that base
* put quantity last until quantity.times() can handle units
add dimensions property to unit set to dimensionality parsed
nameless dimensionless unit to combine u.value and u.aliases in unit.combine()