Add missing percentPlayed field to onPlayBackEnded events

[HumorBaby]

The onPlayBackEnded needed to specify that percentPlayed was a valid
substitution field.

The event allows for (and even provides in the example) a field for percentPlayed:

script.service.kodi.callbacks/resources/lib/events.py

Lines 43 to 47 in d5dfb0e

	'varArgs': {'%mt': 'mediaType', '%fn': 'fileName', '%ti': 'title', '%ar': 'aspectRatio', '%ht': 'height',
	'%wi': 'width', '%sm': 'stereomode', '%se': 'season', '%ep': 'episode', '%st': 'showtitle',
	'%at': 'artist', '%al': 'album'},
	'expArgs': {'mediaType': 'movie', 'fileName': 'G:\\movies\\Star Wars - Episode IV\\movie.mkv',
	'title': 'Star Wars Episode IV - A New Hope', 'percentPlayed': '26'}

yet, this field is never substituted in args.

I used %pp as the two-letter field name despite there already being another %pp for profilePath. These two fields should never collide, so I figured it was okay to do this.

[i3laze]

Will this fix the fact add-on isn’t working in Leia at all? :(