Schema documentation with modified schemaSpy

Note: 
The documentation generated here is not based on the current bety database, but my local copy. The difference is that I have added some of the foreign key constraints (otherwise schemaSpy won't be able to detect any relationship or create diagrams). Currently this application generates multiple pages of output, but I think the only useful ones are index.html, relationship.html and the pages for each table inside the "table" folder. In order to keep it simple I removed some output such as 'parent', 'children' and the one-degree diagrams in the table documentation pages and added some extra conditions for displaying information.