SparkPost Mail Transport for XF 2.3 3.0.4

Minor bugfix to explicitly enforce admin permissions on admincp tools

bugfix - fix a bug in exception handling in AbstractHttpTransport

v3.0.2 addresses a bug in an underlying SparkPost package which resulted in the from header not containing the forum title

Some composer dependencies were missing from the 3.0.0 release, causing issues with bounced email handling on some platforms that didn't already have those dependencies installed via other addons. This release fixes the issue.