Source documentation, English manual

* locco source documentation builds now in build/sourcedoc
  Needed to patch locco for that. First argument is now
  the destination path
* Schema translation and source documentation is now
  made by Rake/Rakefile
* more English documentation (including screenshots)
* New plugin for Jekyll (for images)
* tiny schema update (Value allowed in Textblock)
Remove javascript files not necessary anymore

They originate from node.js based sp implementation
Message translations now handled by rake

Remove obsolete sdcontrol and optionparser.lua which is
only required by sdcontrol
Updated some German translations.