srm: use ordinal numbers for files within container requests

Currently we indicate elements within a container request using the
corresponding ID.  This is needlessly confusing and takes up a lot
of space in logging.

This patch adds support for logging information with the 1-indexed
ordinal numbers.

Conflicts:
	modules/srm-server/src/main/java/org/dcache/srm/request/BringOnlineRequest.java
	modules/srm-server/src/main/java/org/dcache/srm/request/FileRequest.java
	modules/srm-server/src/main/java/org/dcache/srm/request/GetRequest.java
	modules/srm-server/src/main/java/org/dcache/srm/request/LsRequest.java
	modules/srm-server/src/main/java/org/dcache/srm/request/sql/DatabaseFileRequestStorage.java