added slide control buttons
Update gallery.css
Update gallery.js
Update gallery.html
Merge pull request #3 from yi-cheng/patch-3

Patch 3
select images
Merge pull request #1 from yi-cheng/patch-1

Patch 1
Merge pull request #2 from yi-cheng/patch-2

Patch 2
Merge branch 'master' into gallery

Conflicts:
	gallery.html
added play pause
display large image accordingly
basic function done