v1.3.0-criteo-25: Deactivate "select all" checkbox in TaskList (#30)

We had an incident where a user selected all tasks and deleted all his
instances by mistake.
There is no obvious need for this checkbox (individual ones are still
useful of course) so it's simpler to just deactivate it.

Change-Id: I2efe795a97cf45cf6e961a8c7cdc185e753130c4
JIRA: MESOS-3936