Rename `getExistingSequence` to `getSequences`
Rename `getExistingSequence` to `getSequences`

Ref. #6

SkygearIO/skygear-server,rickmak/skygear-server,SkygearIO/skygear-server,SkygearIO/skygear-server,SkygearIO/skygear-server,rickmak/skygear-server,rickmak/skygear-server