Fixed aborting drinking from a keg, polished examining keg contents

Previously, drinking directly from a keg would consume a charge even if the player aborted before drinking, such as if they decided not to drink upon realizing they couldn't finish it. Now a charge is only consumed if the player actually drinks, the same as consuming anything else.

Examining the keg contents now displays number of charges and how full the keg is as a percentage. Previously it did not display charges (unless there was under 250ml left) and displayed quantity only in terms of unlabeled 250ml units. The new way is more consistent with existing fluid containers while still easy to tell at a glance how much space remains.