res:dock:: change applet icon from dock.

1. switch mode.
2. switch theme icon.

tower:https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/2e5603ced09048dc8eb74f44c3c5d553/
tower:https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/5ef98cd230244b44b2236a8510a6f3a8/?proto=https
Change-Id: Ibd584ef601525496e2a2ac9d53659cf4f701a9d6