3610: Move live log display into its own tab, avoid clobbering with tab reload.

* PipelineInstances#show gets a Log tab dedicated to the live log
  window, rather than hiding it below the components table.

* Jobs#show uses its Log tab to show a live log window (instead of a
  teaser) when the log is not yet finished/written to disk.

* In both cases, the live log window's tab pane intercepts and ignores
  the arv:tab:reload event. (Previously, in addition to appending log
  entries to the live window, websocket events would trigger a
  "refresh all tabs" event, which would blow away the whole log viewer
  anyway.)

* Behave sensibly when multiple lines of stderr arrive in a single
  websocket update event.

* Stop displaying "update {pipeline-uuid}" messages that have no
  additional content.

* Stop scrolling to bottom every time an ajax:complete fires
  somewhere. (Previously, seeing anything above the last page of logs
  was somewhere between annoying and impossible.)

* Make the log window taller.
Merge branch '3610-pipeline-log-refresh' closes #3610