Fuze+: add a configurable deadzone area for touchpad buttons

To stop erroneous button presses, allow users to add a deadzone between
the button via the Settings > General > System menu > Touch Dead Zone.

The configuration was chosen this way: the touchpad has the same DPI
in both direction so the setting applies the same on both the X and Y
axis. The setting ranges from 0 to 100 and is internally multiplied by 2
giving a maximum deadzone of 2*100 = 200 around each button, which
account for 400 total (once around each button), effectively reducing
each virtual button from 1000x600 to 600x200 when using the maximum value.

Change-Id: I8683c63d2950200eb32d1dda0a00bbd92d83d5be
Reviewed-on: http://gerrit.rockbox.org/677
Reviewed-by: Benjamin Brown <foolshperson@gmail.com>
Tested: Benjamin Brown <foolshperson@gmail.com>
Reviewed-by: Amaury Pouly <amaury.pouly@gmail.com>

apps/lang/english-us.lang

@@ -10605,6 +10605,23 @@
     gigabeatfx,sansafuzeplus: "Touchpad Sensitivity"
   </voice>
 </phrase>
+<phrase>
+  id: LANG_DEADZONE
+  desc: touchpad deadzone setting
+  user: core
+  <source>
+    *: none
+    sansafuzeplus: "Touchpad Dead Zone"
+  </source>
+  <dest>
+    *: none
+    sansafuzeplus: "Touchpad Dead Zone"
+  </dest>
+  <voice>
+    *: none
+    sansafuzeplus: "Touchpad Dead Zone"
+  </voice>
+</phrase>
 <phrase>
   id: LANG_HIGH
   desc: in settings_menu

apps/lang/english.lang

@@ -10692,6 +10692,23 @@
     gigabeatfx,sansafuzeplus: "Touchpad Sensitivity"
   </voice>
 </phrase>
+<phrase>
+  id: LANG_DEADZONE
+  desc: touchpad deadzone setting
+  user: core
+  <source>
+    *: none
+    sansafuzeplus: "Touchpad Dead Zone"
+  </source>
+  <dest>
+    *: none
+    sansafuzeplus: "Touchpad Dead Zone"
+  </dest>
+  <voice>
+    *: none
+    sansafuzeplus: "Touchpad Dead Zone"
+  </voice>
+</phrase>
 <phrase>
   id: LANG_HIGH
   desc: in settings_menu