Use only SI units in exhange

Description of the proposal:

Use only metric units in IFC. For example, have all length values as meters.

What do we win:

* Reading of IFC is simplified. You don't need to convert from exotic units to your internal units.
* Precision concerns can be thought of in one go: We can advice, for example, how to model very large projects (infrastructure)

What do we loose

* Nothing, the user of the reading application can use whatever display units they want

Schema impact:

* Schema is simplified

Instance model impact:

* Simpler files

Backwards compatible:
* no

Automatic migration possible:
?

Additional implications:
-
Note that not all points need to be satisfied!
Backwards compatibility and file size are not concerns.