Update documentation for explore-* commands

[jivanpal]

The currently spec'd interactive explore-* commands should be changed to non-interactive list* commands, and the interactive exploration functionality should instead be accessible via an --interactive option for each command. That is:

• Abandon explore-fs, retain list (rename explore-fs to list in the docs)
• Rename explore-omap-tree to list-omap-tree
• Rename explore-fs-tree to list-fs-tree

Implementation of the --interactive functionality is deferred to this task: Add interactive modes to list commands