Added Command Line Argument Support

Hey,

I started making some small changes, but ended up doing a lot of stuff, if you're happy with the changes please accept the pull request.

I added these arguments:

makevideo.py:

-o for output directory
-f for movie file name

screenlapse.py

-o for output directory
-t for time interval

Also, added the python3 env, and made the files executable.

Yasith