Fixes to atmosia computers and gas sensors (updated)

__Atmospherics fixes :__ _(updated)_

* Fixed a leftover that was preventing atmospherics computers to actually recieve input from the various sensors in the room.

* Also changed the "output" variable of the gas tanks' sensors, so they actually send data about the gas mixture in each of them.

* Make the atmos computers dialog auto-refresh so you can keep track of the data evolution (pressure rising, gaz mixture changing, etc)

* Formatted the dialog output for better readability

_Before_ : 
![before](https://cloud.githubusercontent.com/assets/7117411/2685718/7162d7c0-c1d3-11e3-8540-a5e156a6f17c.png)

_After_ : 
![after](https://cloud.githubusercontent.com/assets/7117411/2689295/eec2f6fe-c2f6-11e3-9610-0b231bdfdf6e.png)

*  Added an option to initialize a newly built atmos computer to either monitor the distribution loop or the tanks.
Atmos computer are now reconstructable __and__ usable.

![initialize_atmos_comp2](https://cloud.githubusercontent.com/assets/7117411/2689302/ad17055a-c2f7-11e3-8e74-7d8574328f4d.png)

* Make the alert computer dialog refresh when clearing an alert and updated the action text to tell what (area) alert was cleared (#3210).