Fixed a bug where the app halts when running on different screen sizes

Fixed a bug where the app halts when running on different screen sizes

The memo app have some hard-coded property that only works for running in
480x800, 600x1024 and 720x1280.  This causes the program to halt when it
runs in different screen resolution or orientations, since it looking those
non-existing properties causes elementary to throw out errors.  This patch
makes it so that all screen sizes will map to the same height property used
so it is more generic and no longer dependent on certain screen width and
height.

Signed-off-by: Jimmy Huang <jimmy.huang@intel.com>