rework BackgroundCommands:
rework BackgroundCommands:

a new function `executeCommand` to deal with command name, count, ...;
make `count` needed by bg-functions global: => `commandCount`;
abstract calling chrome.tabs.getAllInWindow
replace '.noTab' with `.useTab`
rearrange arguments of functions

gdh1995/vimium-plus,gdh1995/vimium-plus,gdh1995/vimium-plus