[log] Remove obsolete CommitCell & its Renderer
[log] Make it possible to add VcsLogHighlighters to the log table.
[log] Expose VcsLogUI & DataPack to the vcs-log-api

* Introduce VcsLogUi interface to the API & to VcsLogDataKeys
  Provide an instance from the MainFrame.
  Provide information about current filters.
* Introduce VcsLogDataPack, let DataPack implement this.
  Provide information about log providers map.
[log] Introduce VcsLogDataProvider to the API as part of VcsLogDataHolder

* Provide getHash and getCommitIndex methods
  rename putHash -> getCommitIndex: this name looks more clear.
[log] make constants final
[log] repaint ui after adding highlighter
[log] Expose the VcsLogFilterUi to the API, let set filter value

+ Since VcsLogFilterUi gets into API, remove getFilters from VcsLogUi,
  substituting it with getFilterUi().
[log] Expose VcsLogRefs into API

* For now just return branches, since it is all what's needed.
* Keep getRefsModel() until it is decided what methods should be exposed
[log] Add ability to reuse branches filter popup
[log] Add ability to listen to possible filter changes
[log] IDEA-118947 Implement special highlighting for cherry-pick

* Add DeepCompareAction as a toggle action to the vcs log toolbar.
* Clicking on the button starts 'git cherry' in background to
  get commits non picked to the current branch.
* Once completed, the log is highlighted so that picked commits
  appear in grey.
* If initially there is no branch filter or several branches selected,
  propose user to select a single branch, apply filters and start
  collecting git cherry.

* If branch filter changes, reset the highlighting.
* If the log refreshes, restart all procedure to make sure that
  highlighting is correct, say, after cherry-picking on of the "black"
  commits.
* But if current branch changes, reset the highlighting and don't
  restart the procedure.

* DeepComparatorHolder maintains a single DeepComparator instance
  per each VcsLogUi (i.e. each vcs log).
[log] Remake VcsLogJoiner without recursion.
[log] Fix tests. (fix wrong line separators)