Create a .fmu in the correct place if it does not exist

[mferrera]

Functionality should be added that creates a .fmu directory at the root of an FMU project. This issue doesn't describe under what circumstances this occurs, as there might be several:

• The FMUCONFIG forward model can provide a validation check for this (but does not fail on it!)
• FMUCONFIG could just simply make it if it does not exist

It seems most fitting to place this directory in the root of the project folder, i.e

.fmu/
ert/
fmuconfig/
...
rms/
...

but there's a discussion to be had about this.