minor fix

* update comments
* add new lines for good alignment
* TabEx.uc.js: fix typo of property name
* TabHandler.uc.js: fix <Tab> indentations
improve function
rename cryptic name 'doCMD' to clearer 'doCommand'
improve module
optimize registering events for gesture

* activate all the time: the events which should observe that a gesture starts
  and stops.
* activate only while necessary: the events which have only to work in
  progress of a gesture.
abolish disabling original tooltip of target element

* Though this function prevents an original tooltip from overlapping our custom
  tooltip, the original one disappears immediately by mouse moving and can not
  be so hard to see ours. So I decided to remove it.
reuse tooltip that is created once for the same target
observe mousemove event only while trigger keys are down

* avoid useless processing that occurs frequently