Added basic auth to internal OX REST API.

File server.properties is enhanced by two properties:

Specify the user name used for HTTP basic auth by internal REST servlet
Default value is open-xchange. Please change!
com.openexchange.rest.services.basic-auth.login=open-xchange

Specify the password used for HTTP basic auth by internal REST servlet
Default is secret. Please change!
com.openexchange.rest.services.basic-auth.password=secret


Both settings need to be set in order to have basic auth enabled - com.openexchange.rest.services.basic-auth.login and com.openexchange.rest.services.basic-auth.password