Preliminary support for Spring Data persist

- Add new repository model for storing StateMachineContext
  via a new StateMachineRepository.
- New StateMachineRuntimePersister interface to abstract needed
  functionality to do a runtime machine persistence.
- As runtime persistence, as of now, is done via interceptors, define
  JpaRepositoryStateMachinePersist and JpaPersistingStateMachineInterceptor
  to define StateMachineRuntimePersister logic.
- Add new datajpapersist sample demonstrating new concepts.
- Keep tests related to jpa as there's not redis/mongo integration
  implemented in this first iteration.
- As this is going to be WIP until features around this issues
  are completed, docs, etc are not yet added. Also, interfaces and impls
  are subject to change during a process.
- Relates to #423
- Relates to #426
- Relates to #427

spring-statemachine-samples/build.gradle

@@ -121,6 +121,18 @@ project('spring-statemachine-samples-datajpa') {
 	}
 }
 
+project('spring-statemachine-samples-datajpapersist') {
+	description = 'Spring State Machine Data Jpa Persist Sample'
+	dependencies {
+		compile project(":spring-statemachine-boot")
+		compile project(":spring-statemachine-data-common:spring-statemachine-data-jpa")
+		compile("org.springframework.boot:spring-boot-starter-thymeleaf:$springBootVersion")
+		compile("org.springframework.boot:spring-boot-starter-data-jpa:$springBootVersion")
+		compile("org.springframework.boot:spring-boot-devtools:$springBootVersion")
+		compile("com.h2database:h2:$h2Version")
+	}
+}
+
 project('spring-statemachine-samples-monitoring') {
 	description = 'Spring State Machine Monitoring Sample'
 	dependencies {