Enable merging of WrappedStringList between 'bottomscripts' and 'reportime'

Enable merging of WrappedStringList between 'bottomscripts' and 'reportime'

* Fix ResourceLoaderClientHtml to return what it was documented to
  return, a WrappedStringList. It accidentally used the wrong join()
  method, causing it to create a plain string too early.

* Update method documentations from ClientHtml::getBodyHtml to
  BaseTemplate::getTrail for 'bottomscripts', and from
  ResourceLoader::makeInlineScript for 'reporttime'.

* Update BaseTemplate::getTrail to join by new line instead of native string
  concatenation.

This by itself would suffice for the most common case, but in order
to also account for the possibility of extensions using hooks for
'SkinAfterBottomScripts' that concatenate, update bottomScripts()
to pass a plain string to the hook and merge it later.

Change-Id: If0d227cb9db67229a27d489c082db790ea8e3840