Add units to building size and axes distance in project setup dialog

[pachi]

As explained in #70 , building size and axes distance use by default mm, if no explicit unit is used, this is a bit surprising if you have setup other units as preferred (e.g. meters).
As it's possible to use explicit units, maybe this is not the right fix for the issue.

[yorikvanhavre]

It is a general rule of FreeCAD that if you don't specify a unit, millimeters are used. This is subject to discussion, but the main rationale behind this is that a stored expression (for ex. "20m+12"), should always return the same result on every system, no matter what the user's unit is in.
Adding [mm] the way you propose is misguiding I think, because it may induce users to think you cannot use any other unit. Rather, I'd argue the correct way would be to find ways to make all users aware that if you don't specify any unit, mm are always used

[pachi]

Yes, indeed. I'm sure this is not the right fix.
I'm still not familiar with FreeCAD source and haven't investigated it enough, but IIRC many entries do have the used units as suffix. That would be the best option, adding units to the default text.