fix (app grid): Adjust vertical padding to improve 1366x768 display

[jacobgkau]

Reducing the value in this calculation (finding the maximum size that the app launcher should be) forces it to go down to 2 rows tall for 1366x768 displays, which fixes #314.

I checked that this doesn't affect the grid on a 1920x1080 display (it's still 3 rows tall.) We may want to check a couple more resolutions to ensure this doesn't result in an app grid that's too small.

[jacobgkau]

Before (1366x768 and 1920x1080):

After (1366x768 and 1920x1080):

[jacobgkau]

Also, for future reference, .65 (or 65% of the screen) was the largest percentage that worked with 1366x768. Allowing the icons to take up 66% (.66) produced the undesired three rows of icons.