minor fix

* change |var| to |let| or |const|
* rename variables to more meaningful ones
* decent formattings
* update comments
remove class property to set styles

* This class property had been reserved to apply styles by global style sheets.
  But I think that registering style sheets is overdoing for this small script,
  so I removed the needless class name and set styles directly to a style
  property.
declare imported functions at the head
minor fix

* update comment
* declare constant for embedded number
rewrite IMEAware.uc.js

I rewrote this script in my favorite style - no large object module.
There is no major change of feature.

Some small changes;
* remove workaround observation of 'keydown' event
* observe 'compositionend' event for IME off during conversion
* use |ucjsUtil.Timer|