Enhance introduction template, create own module

[s-blu]

Describe the inconvience or problem you want to solve or detail the origin of your idea
Currently, the introduction is part of the documents module and displayed if no document is chosen. This should be separated from each other.
Also, the introduction is not very welcoming currently. Formatting and text could be better & more helpful

Describe the solution you'd like

• Create a separate module for introduction stuff
• Load it on / route, put documents to /document route (if possible without Refactor document components (editor and note items) to work with route params #165 )
• Add nicely formatted, more informative text to introduction html's