Recording stats layout customizable.

Users can select the order, visibility and importance (primary or secondary) of all stats for recording layout from the Settings.
Also, users can select the number of columns per row in the recording layout: 1, 2 or 3.
Finally, show altitude/coordinate from settings have been removed (not needed anymore).
Fixes #659.
Fixes #302.
Fixes #820.

doc/data-structure.txt

@@ -43,7 +43,6 @@ class TrackPoint {
     - sensor_power
 }
 
-
 class Marker {
     - id
     - trackId
@@ -58,6 +57,26 @@ class Marker {
     - photoUrl
 }
 
+class DataField {
+    - key
+    - title
+    - isVisible
+    - isPrimary
+    - isWide
+}
+
+class StatisticData {
+    - value
+    - unit
+    - description
+}
+StatisticData o-- DataField
+
+class Layout {
+    - profile
+}
+Layout "1" o-- "many" DataField
+
 note left of TrackPoint
 As of OpenTracks version 3.15.0, all times are using device time.
 Before that TrackPoint.time contained GPS time (determined by GPS hardware).
@@ -77,4 +96,4 @@ Trackpoints of Type.SEGMENT_START_MANUAL or Type.SEGMENT_END_MANUAL do not conta
 
 Tracks recorded prior to OpenTracks version 3.15.0, do neither begin with a Type.SEGMENT_START_MANUAL nor end with a Type.SEGMENT_END_MANUAL.
 end note
-@enduml
+@enduml