Refactored component detail page

[awolkers]

• Changed the way how sourcecode was added to a component detail page. In the old situation only the source of the corresponding html file was automatically added. Now you can add multiple sourcecodes from various file types. You can do this by adding the files you want to include to the components .yml file.

viewsource:
  - nav.html
  - nav.scss

• Added component specific title to component detail page.
• Changed layout file used for the component demo page. This is now the same one as used for the templates. This is done because there was no difference between these files.
• A {{ baseUri }} variable is now available in both the template and the documentation files. The absolute path is changed to a relative path. This change will fix issue Static files only work in a website's root folder #60
• Fixed issue where the browser refreshed multiple times when a component, layout or template file was changed.
• Fixed ESlint errors in config.js file.
• Added example code for adding variables to a component demo page via a .yml file. The functionality was already there but it wasn't documented.
• Changed names of some files and variables from preview to demo. This is now more consistent with the rest of the code.

[sanjaytwisk]

In general I think this pull request is too large. Fixing the ESLint issues, browsersync issue and the relative path issue should have their own pull request

[waarissyb]

I agree with @sanjaytwisk. The committed changes should be as small as possible. Roughly every issue needs its own pull request.

The info that’s added in this pull request should preferably also be written inside the commit. When opening the pull request, you don’t have to type what you’ve done.