code cleanup and replace raw types by generics

* various code cleanup improvements
* replace raw types by generics  (#BATCH-1914): this also uncovered 3 bugs (I think) in following classes:
SkipListenerAdapter, JsrFaultTolerantChunkProcessor and JdbcPagingItemReader (in a dead code path though)

Each item is in a seperate commit so you can pick and choose which ones you want to merge.