lax #5482 customise about / changelog text for lax [open]

currently the content is defined in some files under the ginco/web/views/wdoc/ directory. We should find a way to make files under this directory overridable with files from ginco/goa/wdoc (the easiest way is probably to deal with this in goactl).

Once done we should have custom content for about / changelog under the gae environment.