TI API: resource modification while action is still in progress

[FabrizioMoggio]

Problem description

• there is no error handling if the API Consumer invokes the TI API for the same Device-AppId if the previous requests are not completed yet.
• the modification of the resource is expected to be done via PATCH but this is not well define din the documentation

Expected behavior

• improve error handling considering to provide back an error code if the status of the previous action on that Device/AppId is not yet "active".
• improve documentation
• suggest to use Patch to modify a resource instead of creating a new one for the same Device-AppId

Additional context
If, the status of the first resource is "active" and the API Consumer, to modify the routing, instead of using a PATCH, creates a new resource with another POST, this is allowed and the new resource will overrule the previous one.

[FabrizioMoggio]

Fixed with: #296

[FabrizioMoggio]

PR merged