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

spring-session-data-gemfire/build.gradle

@@ -0,0 +1,22 @@
+apply from: JAVA_GRADLE
+apply from: MAVEN_GRADLE
+apply plugin: 'spring-io'
+
+description = "Aggregator for Spring Session and Spring Data GemFire"
+
+dependencies {
+    compile project(':spring-session')
+    compile("org.springframework.data:spring-data-gemfire:$springDataGemFireVersion") {
+        exclude group: "org.slf4j", module: 'slf4j-api'
+        exclude group: "org.slf4j", module: 'jcl-over-slf4j'
+    }
+    runtime "org.springframework.shell:spring-shell:1.0.0.RELEASE"
+}
+
+dependencyManagement {
+    springIoTestRuntime {
+        imports {
+            mavenBom "io.spring.platform:platform-bom:${springIoVersion}"
+        }
+    }
+}