Implementation of StateModelDef access in rest 2.0

[kaisun2000]

Current implementation of Rest 2.0 does not support stateModelDef modification. Here, we will implement

delete -- remove the stateModelDef with the input id.

put -- create new statemodeldef if no existing one with same input id

set -- replace the content of node with input id

[huizhilu]

@kaisun2000 Are you working on this? If not, I am considering to contribute to this ticket. Thanks.

[kaisun2000]

#339 has a diff for the implementation, pending review

[huizhilu]

I saw the diff right after leaving the comment. Thanks.

[kaisun2000]

Code merged into #339.