[log] Copy hash action

Use "Ctrl/Cmd+C" shortcut.
Copy a single long has, or multiple ones separated by newlines.
[log] Special "me" value for the user filter

* On Vcs Log initialization read current user name for all roots,
  and store them in a map.
* Use a special VcsUser class to identify the user.
  It has just the username for now.
* Add a special "me" value to the user filter component.
* Let VcsLogUserFilter be a superclass of two different cases: when a
  user is selected by name, or when "me" is selected.
  Since "me" can be different for different roots, let getUserName()
  accept the root parameter (used from the GitLogProvider).
[log] Split VcsLogSettings

Introduce VcsLogUiProperties (without interface in vcs-log-api,
since it is an internal class) to hold such details of user activity
as "does he prefer to see details or not", "what are his recent
filter values", etc.
[log] Remember users which were recently used in the user filter.