standardize file names and use file name as description

[JannisBush]

At the moment all files have non standardized names, e.g. experiments/introduction.markdown, experiments/02filestructure.markdown and overview/introduction.markdown, introduction/advantages.markdown.

Also, some displayed names are not identical to their file names, e.g. resources and reuse on the top level. Or the page title and the sidebar title is not identical, e.g. Introduction and Overview under the experiments tab.

This makes it harder to find files and to navigate the homepage.