[colorful-home] Avoid painting the lockscreen when off-screen

Due to QtQuick1's not very good rendering logic, the lockscreen will be
painted even when off screen, which can cause lag if a too-big wallpaper
is used.
[colorful-home] Improve lockscreen logic and animations

Improved the lockscreen to use separate animations for snapping open or
closed, cleaned up the lockscreen positioning logic, and fixed several
corner case bugs with the lockscreen position.
[colorful-home] Reset the homescreen page when locked
Merge pull request #15 from special/master

Improve lockscreen behavior