Switch BufferingStompDecoder to decoration

The BufferingStompDecoder now decorates rather than extend
StompDecoder. This allows a single StompDecoder instance to be
configured and extended independantly while buffering remains a
separate concern.
Polish ResourceDatabasePopulatorTests
Add strategy for customizing ID/TIMESTAMP headers

Introduce MessageHeaderInitializer strategy for initializing a
MessageHeaderAccessor.

Add IdTimestampMessageHeaderInitializer implementation that provides
control over ID and timestamp header generation.

Disable ID and timestamp by default in SimpMessageHeaderAccessor and
therefore its sub-class StompHeaderAccessor.

Issue: SPR-11468
Use strategy for customizing ID/TIMESTAMP generation

Issue: SPR-11468