editorial: List all data associated to a platform sensor in one place

Previously, part of the data associated with a platform sensor was listed in
the "Concepts" section and the rest was listed in the "Model" section, which
made it confusing to follow.

Keep the definitions listed in the "Concepts" section there, but also
reference them in "Model" so that the latter contains all data associated
with a platform sensor.

This commit is marked as editorial because it only reorganizes existing
definitions.

Related to #463.

index.bs

@@ -800,12 +800,12 @@ A [=sensor type=] may have the following associated data:
 
 <h3 id="model-sensor">Sensor</h3>
 
-The current [=browsing context=]'s [=platform sensor=] must have:
-- An associated [=ordered set|set=] of <dfn>activated sensor objects</dfn>,
-  which is initially [=set/is empty|empty=];
-- An associated <dfn>latest reading</dfn> [=ordered map|map=], which holds the
-  latest available [=sensor readings=].
-- An associated [=sensor type=].
+A [=platform sensor=] must have the following associated data:
+- A [=sampling frequency=] (a number), initially 0.
+- A [=device sensor=] to which it is connected or null, initially null.
+- A [=ordered set|set=] of <dfn>activated sensor objects</dfn>, which is initially empty.
+- A <dfn>latest reading</dfn> [=map=], which holds the latest available [=sensor readings=].
+- A [=sensor type=].
 
 Any time a new [=sensor reading=] for a [=platform sensor=] is obtained and if the user agent
 [=can expose sensor readings=] to the current [=/navigable=]'s [=navigable/active document=],