Script to make adding images easier

Here's a script that I've been using to add new images to the project and database.  It runs the convert.py, creates a CSV, runs the db-tools.py and deletes the out/ and CSV at the end.  

So to add a new image, I run this one-liner

    python scripts/add-image.py -f /home/username/Desktop/angry_grumpy_cat_good.png -c Angry

It doesn't increment the version number though.  

I've also modified the README.md and referenced the add-image.py in the 'easy mode' section.  

I'm putting this in a pull request in case you find this useful.  If not, no worries!