Add "Kill" and "Kill & Scale" buttons for tasks

Make task rows clickable in order to "Kill" and "Kill & Scale".
Multiple tasks can be killed at once, but kill & scale is currently
only implemented for one task at a time due to issue
https://github.com/mesosphere/marathon/issues/108. By allowing
only one at a time, it throttles the requests and ensures the
scaling happens properly.

Also make all table rows look clickable with pointer cursor since
they are actually clickable.