create reset function for findbar
reset state for new text of common findbar
fix wrong function name
make |getTabs| function return all tabs too
improve |createNode| function

* does not set attributes for an empty string value.
* removes attibutes with |null| value.
* an attribute handler accepts all values including |undefined|.
count only visible tabs to show proper tabs sum
test whether string value is exist or not
refactor code with utility handler for browser windows
refactor handling for command of menuitem

* observe the command event to perform a custom command
* remove |ucjsUtil.focusWindowAtIndex| function that was exposed only for this
  script.
scan only visible tabs to list opened tabs
make module of functions for places DB
make module of functions for session store
fix missing favicon of closed window
enclose local constants in thier scope
rearrange code with enhanced utility functions
minor fix

* rewrite conditional branches for readability
fix history error for unloaded document of duplicated tab
support command with modifier keys for submit mode
single out command function with usage for readability
use reliable alias for content window