Need com.googlecode.jsonrpc4j.spring.rest.JsonRpcResponseErrorHandler fixing

[im-scooter]

1. JsonRpcResponseErrorHandler - has been designed as enum, so it cann't be extended. For example for procesing specific http errors (as example 401)

2. method getResponseBody() process response (for example HTTP 401) incorrectly when HttpUrlConnection works in streaming mode.

java.lang.RuntimeException: cannot retry due to server authentication, in streaming mode
at com.googlecode.jsonrpc4j.spring.rest.JsonRpcResponseErrorHandler.getResponseBody(JsonRpcResponseErrorHandler.java:92) ~[jsonrpc4j-1.5.0.jar:1.5.0]
at com.googlecode.jsonrpc4j.spring.rest.JsonRpcResponseErrorHandler.handleError(JsonRpcResponseErrorHandler.java:64) ~[jsonrpc4j-1.5.0.jar:1.5.0]
at org.springframework.web.client.RestTemplate.handleResponse(RestTemplate.java:700) ~[spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:653) ~[spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:613) ~[spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
at org.springframework.web.client.RestTemplate.postForObject(RestTemplate.java:380) ~[spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
at com.googlecode.jsonrpc4j.spring.rest.JsonRpcRestClient.invoke(JsonRpcRestClient.java:216) ~[jsonrpc4j-1.5.0.jar:1.5.0]
at com.googlecode.jsonrpc4j.spring.rest.JsonRestProxyFactoryBean.invoke(JsonRestProxyFactoryBean.java:92) ~[jsonrpc4j-1.5.0.jar:1.5.0]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.7.RELEASE.jar:4.3.7.RELEASE]

[gaborbernat]

@im-scooter feel free to create a PR. At the moment I'll accept PRs and release them, however my focus has shifted away from this project otherwise.

[im-scooter]

pull request #175