SPARK-1890 and SPARK-1891- add admin and modify acls

It was easier to combine these 2 jira since they touch many of the same places.  This pr adds the following:

- adds modify acls
- adds admin acls (list of admins/users that get added to both view and modify acls)
- modify Kill button on UI to take modify acls into account
- changes config name of spark.ui.acls.enable to spark.acls.enable since I choose poorly in original name. We keep backwards compatibility so people can still use spark.ui.acls.enable. The acls should apply to any web ui as well as any CLI interfaces.
- send view and modify acls information on to YARN so that YARN interfaces can use (yarn cli for killing applications for example).
yes it requires it set before.  I went back and forth on this a bit and choose to keep it this way since its private and only really called in once place at this point (history ui).    And actually only the view one is called the modify one isn't called anywhere outside of this class.  We could add the additional logic but I kind of see it as just overhead right now.  Normally everything is initialized just when you create the securityManager and so these routines aren't called outside of here. 

I could be swayed to change it. I should atleast add a comment here also.  I have it in some other places, but should add here too.