Flexible command executor configuration

See http://jira.codehaus.org/browse/ACT-1758.

Spring and JTA QA now succesfully pass with MySQL.

Added ability to flexibly configure the command interceptor chain by moving their configuration from the interceptors themselves to CommandConfig. Related simplification of the command-executor related functionality. 

CommandExecutor split into seperate CommandExecutor and CommandInterceptor interfaces. CommandExecutor now has 2 execute methods, 1 with and 1 without the CommandConfig. CommandInterceptor only has the one with CommandConfig. CommandExecutorImpl renamed to CommandInvoker.