Adding the "Playing with Blocks" section.

This section focuses on indexing, for-loops, if-statements, and slicing.
Adding the "Building Blocks" section.

This covers reading files and introduces lists and strings.
Adding animation frames and notebook used to create them.
Moved the section learning goals into their respective sections.
Added functions and glob to Building Blocks section.
Renamed README to instructor_notes and added new general README.
Copying in latest version of ipythonblocks (@a3bfc2c).
Importing colors dict into the notebooks.
Adding sections on elif and slicing.