0.17.3: Merge pull request #154 from noobLue/master

change

• improved the caching logic for C# runner and maven
• updated maven to 3.8.1
• moved bundled maven location from tmc/apache-maven-3.6.3 to tmc/apache-maven
• added progress tracking to paste
• improved dl tracking message
• changed prepare-submission to prefix the submission zip contents with the course and exercise names

fix

• clippy lints
• added back progress tracking to dl

etc

• documented course-wide tmcproject files
• improved docks for sandbox_image in tmcproject