Easy install of requirements

Added easy installation of dependencies with requirements.txt file.

Also minor updates to notes (L5 and L6 context management) and syntax update for the L9 GUI example.

Minor Notes Update

Added note and example to L4 notes about default argument single-initialisation, and the possible issues of modifying and/or returning mutable default arguments.

Licensing Update

• Updated license of testing module (TestRun.py) to be excluded from external license, and include private internal license to reduce restriction of its use outside the course
• Added useful feature list to testing module, to improve its usability, particularly outside the course context
• Updated L4 notes about positional arguments to include a better example

Minor Fixes

• Fixed an omission in function syntax default arguments (L4), and
• Updated L10 to include GitHub's updated policy of free private repositories.

Admin Update

Fixed version number in README, and a couple of spelling mistakes.

Minor Updates

Updated the lesson 9 notes to cover more options for installing packages (with PyPI).
Removed an unnecessary file.

Course Official Release

Official release of this python 3 and programming principles course.

Includes detailed lesson notes, exercises, automated tests, example solutions, and links to external resources for those who want to know more.