Moved "action links" from LogEventsList to LogFormatter.

Moved "action links" from LogEventsList to LogFormatter.

* This allow extensions to set both action text and links directly
  from a subclass LogFormatter instead of having to use the LogLine
  hooks for this purpose.
* Moved stuff for logs that already use a subclass of LogFormatter
  there and the remaining in LegacyLogFormatter. I had to an hack
  there so that the pass-by-ref of the comment parameter in the
  LogLine hook still works.
* Removed RevisionDeleter::getLogLinks(), included it directly in
  DeleteLogFormatter::getActionLinks(); it have a so ugly signature
  that is very hard to use it somewhere else (and maintain backward
  compatibility too).
* Removed the message caching system in LogEventsList since it's
  not used anymore.
* Some misc cleanup to LogEventsList::logLine()

Change-Id: I96d696eed2ae35f5f5640e422ceb0a5b0c33babf