[log] DfsUtil: use IntStack.
[log] Drop unnecessary method from PermanentGraphLayout.
[log] Add IntTimestampGetter.
[log] Add PermanentCommitsInfo.
[log] Create new internal graph api.

Add GraphWithHiddenNodes as PrintedGraph and GraphWithCommitInfo.
[log] Remake PermanentCommitsInfo with CommitId.
[log] Remake PermanentGraphBuilder to PermanentLinearGraphBuilder with CommitId.
[log] Add draft of PermanentGraphImpl.
[log] PermanentGraphLayout -> GraphLayout.