logcmdutil: drop redundant "log" from function names (API)
A few exceptions:
- s/loglimit/getlimit/ to avoid name conflict
- s/_logrevs/_initialrevs/ to clarify its functionality
logcmdutil: rename classes and functions to conform to our coding style (API)
show_changeset is renamed to changesetdisplayer as its return value is called
a displayer.