Remove unused code in redis aggregate counter.
Reworked exception handling code to add more precise causes
Applied changes following mpollack's comments
XD-368: Improve redis connection use in aggregate counter

Implemented as a single action using a RedisCallback.
XD-348 Add fixed delay interval for job execution scheduler task
 Added fixed-delay scheduler task config
 Updated JobPlugin to process module with "fixed-delay" property key
 Added test to check IntervalTask bean is added to the module application context
Added Enumeration to support common naming for modules vs. strings.
Added AbstractPlugin class to add tooling for common tasks of a plugin.
Moved BeanDefinitionAddingPostProcessor from Dirt to module so that it can be accessed
Created Plugin package under module project and moved all plugin based classes and interfaces to the package.
Updated the IntegrationPlugin to use the AbstractPlugin.
Cleaned up the BeanDefinition docs.
Updated to simplify Plugin development
for modules.
Merge branch 'XD-357' of github.com:cppwfs/spring-xd into XD-357

Conflicts:
	spring-xd-dirt/src/main/java/org/springframework/xd/dirt/plugins/job/JobPlugin.java
	spring-xd-dirt/src/test/java/org/springframework/xd/dirt/plugins/job/JobPluginTests.java
Updated code per code-review requests.