Clean up thumbar (thumbnail) code (#670)

* Cleanup thumbnail bar code

- rename thumbnail method names for succinctness
- Get rid of 'updateThumbnailBar' event -- use existing events
- Get rid of 'blockPowerSave' and 'unblockPowerSave' events -- use a
new combined 'onPlayerPlay' and 'onPlayerPause' events which apply to
power save and updating the thumbbar

* Consistent naming for enable/disable methods

main/menu.js

@@ -16,7 +16,6 @@ var config = require('../config')
 var dialog = require('./dialog')
 var shell = require('./shell')
 var windows = require('./windows')
-var thumbnail = require('./thumbnail')
 
 var menu
 
@@ -34,8 +33,6 @@ function onPlayerClose () {
   getMenuItem('Increase Speed').enabled = false
   getMenuItem('Decrease Speed').enabled = false
   getMenuItem('Add Subtitles File...').enabled = false
-
-  thumbnail.showPlayerThumbnailBar()
 }
 
 function onPlayerOpen () {
@@ -47,8 +44,6 @@ function onPlayerOpen () {
   getMenuItem('Increase Speed').enabled = true
   getMenuItem('Decrease Speed').enabled = true
   getMenuItem('Add Subtitles File...').enabled = true
-
-  thumbnail.hidePlayerThumbnailBar()
 }
 
 function onToggleAlwaysOnTop (flag) {