This was previously hard-coded to "exports", which is so named because the
system is currently used only to export data to another system.
This change retains the previous functionality.
* src/server/daemon/controller.js (_initExportService): Pass new TokenDao
argument.
* src/server/token/TokenDao.ts (TokenDao)[_rootField]: New property.
(constructor, getToken, _genRoot): Use it.