pour liquids into containers on ground

Pour some liquid from inventory to near tile with *containers*.

* Old behaviour: liquid pours on ground.

* New behaviour:
![pour](https://cloud.githubusercontent.com/assets/6351438/3560592/a6fd3758-0978-11e4-88db-05ca3879d187.png)

upd: interface and behaviour changed. Look in comments for info.
Just checked this with "./lang/update_pot.sh", the second text won't be extracted for translation. You have to write something like
```
add_msg(on_ground ? _("You pour %s into %s.") : _("You pour %s into your %s."), ...
```