Swipe from center to better compatible with all sizes of screen

[tankery]

Swipe from center instead of swipe from corner, can help deal with the case that target page has a title bar or scrollable area is not full screen.

This change even let it support mobile devices

The swipe algorithm is:

1. read screen size of device
2. swipe start from screen center
3. swipe up for 1/4 of screen height each time

PS: I've tested the modified script on a 400x400 Wear OS device, and a 1080x1920 mobile device.