reconstruct the dock applets manager frame to make it more flexible

NOTE: read README.md to see how to write a valid applet

tower: https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/4934209cab0c4a259be123642e27ea59/

Change-Id: I56593fe3d129991ea7f4b6d31b783ec739222ef5