manage TOC generation over portalconfig

Many projects don't want the Table of Contents (TOC) in the TextGrid portal for various reasons. In some cases the generated TOC is not very good (e.g. the links don't work), in other cases the generation of the TOC leads to various problems when rendering the HTML page. This is the case with the Shakespeare project.

The idea is to give projects the option to enable or disable the TOC via the portalconfig file. Perhaps the default option should be not to generate the TOC, and only projects that enable it via portalconfig would get this option.