fix cors issue

Motivation:

CORs is a technique that uses additional HTTP headers to inform browsers to give a client application at a particular origin access to requested resources at a different origin. This was previous implemented but needed some few adjustment to make it work.

Modification:

• Change the property name for allowed origin from cerebrum.allowed.client.origins to cerebrum.allowed.origins Hence it can be set in the command line as follow: java -jar --cerebrum.allowed.origins=<comma-seperated-values>
• Add OPTIONS method to the list of allowed methods and obtain the value of the property: cerebrum.allowed.origins

Result:

CORs now works

Target: master