Move delivered directory structure to automatic creation via initialize

[cliffparnitzky]

Since Contao 4 there is a general problem with the delivered directory structure for the documents.

This will be symlinked from files directory to vendor.

• This is on the one hand not very pretty.
• When updating the dms this directory structure will be delete, so all document files will be lost.
• When deinstalling the extension, all files will also be lost.

The initialize process should create the default structure in the files directory. This should avoid these problems.