Settings : Update gesture preference check

Move the gesture outside the stylus dependency check and remove the
preference category if no children are found

Change-Id: I05ecf71dc84f5244200e3030b5ee524944339145
(cherry picked from commit f6a43a4bc50f6fba64f55c08adff16f8bdcb1c44)
Dont show "Erase SD Card" when there is none

On devices with physcal, external SD Cards, the "Erase SD card"
option in in Settings/Storage is available even when there is
no SD card present, this dont make much sense since you cannot
erase a card that is absent. With this change the erase option
is bound to the mount toggle which leads to the following
consequences:

 Card present and mounted -> Erase enabled
 Card present but unmounted -> Erase enabled
 No card present -> Erase disabled
 Card present and MTP attached -> Erase disabled

Change-Id: I756ae8af3e0565febaf940df5f4991dd89105bd9