Fix style consistency

[ppanero]

The training contain many consistency issues in term of styling. Many of them have been address by @topless in the PRs mentioned here #81. Note that the issue has been closed since the changes of those PRs have been partially merged as part of #82. Nonetheless, the PRs are left open due to the extra changes.

Some of the issues:

• $ at the begginng of the commands. This might cause errors when copying.
• The type of codeblock used along the trainings varies betweenbash, commandline (e.g. tutorial 6) and console (e.g. tutorial 13). However, it is not clear when to use which.
• Copyright should be updated 2019 to 2020
• Python 2 __future__ imports.
• The records mappings' folder present in the solutions is not a python module. It has missing __init__.py files.
• Using * vs - for enumerations. Even though at display time there is no difference.

reference markdown lint rules