ENH Add branches to supported modules list

[GuySartorelli]

This is needed for systems that need to know which branch to grab from github, e.g. api.silverstripe.org

Other changes

• Small fixes in the readme (list cow as a repo that uses this, standardise formatting for "format" items)
• Fix "type" for some items (modules should be listed as modules, non-modules should be listed as dependencies - though there is some nuance here since cow's idea of "module" is perhaps different to the common understanding)
• Remove items that shouldn't be in the list (not CMS 3 compatible) and add items that should be (based on https://www.silverstripe.org/admin/pages/history/show/2110/85)

Issue

• api.silverstripe.org only has core modules api.silverstripe.org#104