Refresh the emoji library (#7001)

* refresh the emoji library

* fix img_trans.gif

* compress sprite sheet

* remove note on compression - webpack seems to handle compression decently

* better emoji sheet preloading

* requested changes

webapp/Makefile

@@ -1,4 +1,4 @@
-.PHONY: build test run clean stop check-style run-unit
+.PHONY: build test run clean stop check-style run-unit emojis
 
 BUILD_SERVER_DIR = ..
 
@@ -54,3 +54,6 @@ clean:
 	rm -rf dist
 	rm -rf node_modules
 	rm -f .yarninstall
+
+emojis:
+	./make-emojis