logout should redirect to a configurable route/path

[splendido]

Currently AccountsTemplates.logout() redirects to the configured homeRoutePath.
See this line

Possible solutions:

1. Another configuration parameter (say logoutRedirectPath) to allow for custom redirection.

2 .Doing something like it was done with ensureSignedIn (see this commit): add logout among the configurable routes so to be able to leverage the redirect field of the options. This would be the second fake route for which most of the options are ignored...

[splendido]

now onLogoutHook can be used to override the default redirect to homeRoutePath