Mark aspectj package import as optional and other Import-Package fixes

Currently directmemory-cache component has required imports for Aspectj and also versioned imports for other packages. This causes issue in using it in OSGi env where these dependencies are not present. Would suggest following changes in package imports

• Make org.aspectj* as optional - Cache component can be run without AspectJ
• Change Guava package version range to [9.0,15) - It runs fine with latest Guava v14
• Change slf4j package version range to [1.6,2) - Allows the module to be used in env which use older version of slf4j API