Rename all levels

[holke]

In relation to #87 i renamed all levels, so that they do not have a number in their title anymore and it is easier to change their order now. We renamed

Level1 -> Levelgethome Level2 -> Levelsupermarker Level3 -> Leveldisco

• Renamed all strings with "evelNUMBER" to "evelNAME".
• Renamed all files with "evelNUMBER" to "evelNAME".
• Added a bash script that can do this semi-automatically.

This merge request touches almost every file, so please check carfully. We should also integrate it rather sooner than later, so that we can use the new level identifiers in future.

[holke]

Note: This will not entirely close issue #87, but is a first step.