(GH-58) [module/svn] Add svn module skeleton
[execution] Pass #execute options to systemu invocation

This allows callers to pass things through like :cwd.
(GH-58) [module/svn] Build out basic status checks
[module/svn] svn status should check URL and revision
[module/svn] Test coverage for installing svn modules
[module/svn] Allow svn modules to be reinstalled/updated
[module/svn] Add SVN as a real module type
[module/svn] Run `svn checkout` in correct directory
[spec/system] Extract provisioning steps to mixin
[module/svn] Add system test coverage