LOGBACK-833 - allow previously defined properties (in local scope) to be seen...

LOGBACK-833 - allow previously defined properties (in local scope) to be seen by SiftingJoranConfigurator
 * implemented part two of Ceki's suggestion
 * add getCopyOfPropertyMap() to the PropertyContainer and thus InterpretationContext
 * use local properties that are ineffect at time of creation of SiftingAppender to seed the properties map used when creting the child appenders and properties
 * removed some generics warnings
 * in AppenderFactoryBase use List.subList() rather than "copy whole array then delete and re-shuffle elements"