Medbay/Genetics machinery fixes

Some general fixes for Med/Gen machinery :

* Prevent being able to open/close/interact sleepers, cryo tubes and DNA scanners when in various conditions (weaken, ...) and by non-humans/non-silicons.

* Fixes possibles infinite loops runtime (fixes #5527)

* Added icon updating on power changes/maintenance to Cryo Tubes and DNA Scanners.

_New unpowered icon for DNA Scanners, courtesy of Nienhaus :_
![2014-11-01_19-40-52](https://cloud.githubusercontent.com/assets/7117411/4872876/d415974a-61f6-11e4-906e-ae8b590bc16b.png)

* Unpowered DNA Scanners can no longer be used even if the associated computer is powered

* Cryo cells and sleepers won't work when powerless anymore.
Same with cloning pods and DNA Scanners used by cloning computers.

* Added an "is_operational" proc to machinery instead of duplicating the same check over and over (only asks to expand to the rest of machinery !)