simplify block label code
Cleanup to startTurtle block
stop turtle block, needs the turtle name as arg.
Merge pull request #49 from ignaciouy/stop-turtle

Stop turtle
show errormsg if the turtle is already running.
Merge pull request #50 from ignaciouy/stop-turtle

show errormsg if the turtle is already running.
clean up formatting and turtle x, y code
move highlight code into Block class
adjust label position