Mixed lbs/Kg equipment

[yrinkel]

Many gyms have some equipments marked in lbs and others in Kg.
It would be very nice if Liftosaur would natively support mixed units.

From a coding perspective this could be done by having converting everything to a small internal unit (such as grams) for calculations and rounding back to the unit set for that equipment.

For an extension of that idea, see the Plate pools / sharing of plates idea:
#143 (comment)

Edit: just noticed this idea had been populated already by the author here:
#134 (comment)

Closing this one to avoid duplicates