Rework cpuShares into cpuQuota

cpuShares is the relative weight wrt other apps. This is used when
there is contention for CPU. If we want this, maybe we implement
a UI where we show all the apps and let the user re-order them.
As it stands, it is confusing.

cpuQuota is a more straightforward "hard limit" of the CPU% that you
want the app to consume.

Can be tested with : stress -c 8 -t 20s

dashboard/src/translation/en.json

@@ -1500,8 +1500,8 @@
             },
             "cpu": {
                 "setAction": "Set",
-                "title": "CPU Shares",
-                "description": "Percent of CPU time when system is under heavy load."
+                "title": "CPU Limit",
+                "description": "Maximum percent of CPU app can use"
             }
         },
         "storage": {