Add GemFire Support

Fixes GH PR #148 and PR #308 implementing a GemFire Adapter to support
clustered HttpSessions in Spring Session.

* Resolve SGF-373 - Implement a Spring Session Adapter for GemFire backing
a HttpSession similar to the Redis support.
* Add Spring Session annotation to enable GemFire support with
@EnableGemFireHttpSession.
* Add extesion of SpringHttpSessionConfiguration to configure GemFire using
GemFireHttpSessionConfiguration.
* Add implementation of SessionRepository to access clustered, replicated
HttpSession state in GemFire with GemFireOperationsSessionRepository.
* Utilize GemFire Data Serialization framework to both replicate
HttpSession state information as well as handle deltas.
* Utilize GemFire OQL query to lookup arbitrary Session attributes by name,
and in particular the user authenticated principal name.
* Implment unit and integration tests, and in particular, tests for both
peer-to-peer (p2p) and client/server topologies.
* Set initial Spring Data GemFire version to 1.7.2.RELEASE, which depends
on Pivotal GemFire 8.1.0.
* Add documentation, Javadoc and samples along with additional Integration
Tests.

Fixes gh-148

samples/httpsession-gemfire-clientserver-xml/src/main/webapp/WEB-INF/web.xml

@@ -0,0 +1,55 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
+		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
+	<!--
+	- Location of the XML file that defines the root application context
+	- Applied by ContextLoaderListener.
+	-->
+	<!-- tag::context-param[] -->
+	<context-param>
+		<param-name>contextConfigLocation</param-name>
+		<param-value>
+			/WEB-INF/spring/session-client.xml
+		</param-value>
+	</context-param>
+	<!-- end::context-param[] -->
+
+	<!-- tag::springSessionRepositoryFilter[] -->
+	<filter>
+		<filter-name>springSessionRepositoryFilter</filter-name>
+		<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
+	</filter>
+	<filter-mapping>
+		<filter-name>springSessionRepositoryFilter</filter-name>
+		<url-pattern>/*</url-pattern>
+	</filter-mapping>
+	<!-- end::springSessionRepositoryFilter[] -->
+
+	<!--
+	- Loads the root application context of this web app at startup.
+	- The application context is then available via
+	- WebApplicationContextUtils.getWebApplicationContext(servletContext).
+	-->
+	<!-- tag::listeners[] -->
+	<listener>
+		<listener-class>
+			org.springframework.web.context.ContextLoaderListener
+		</listener-class>
+	</listener>
+	<!-- end::listeners[] -->
+
+	<servlet>
+		<servlet-name>session</servlet-name>
+		<servlet-class>sample.SessionServlet</servlet-class>
+	</servlet>
+
+	<servlet-mapping>
+		<servlet-name>session</servlet-name>
+		<url-pattern>/session</url-pattern>
+	</servlet-mapping>
+
+	<welcome-file-list>
+		<welcome-file>index.jsp</welcome-file>
+	</welcome-file-list>
+</web-app>