BATCH-1908. 

Added batch inserts to JdbcExecutionContextDao and JdbcStepExecutionDao. 
Added JobRepository.addAll(Collection<StepExecution>).  SimpleStepExecutionSplitter calls this method now.  

Note: This change is not backward compatible since any existing JobRepository implementations must implement addAll() now.  

Also did some refactoring in JdbcStepExecutionDao since there are 17 parameter values and corresponding types in the Insert statement, I wanted to avoid duplication. It's not as clean as I would like, but I haven't thought of a better way to do it.