Name and order the build queue code

The queue of the node builds is BuildQueue in build_queue.go, and its
other names start with build: buildMax and buildLeafWindow are its
limits, and BuildMergeHeap holds its merges. The Telegram bot has a
queue of events too, so a bare queue does not tell which one it is.

The declarations of the queue file follow the order of the go-code
skill. The behavior does not change.

Issue: 947bddb