Revert "Added ability to set RaygunLogWriter via _config as well as _ss_environment (_config gets preference)"

This reverts commit 4f767d65cc9c9bb8742e8ec381d893763e355770.
Fixes case where SS_Log::log() is called with a string argument, rather than an array, resulting in a overridden Exception being sent to Raygun, which masks the real error
Revert "Revert "Added ability to set RaygunLogWriter via _config as well as _ss_environment (_config gets preference)""

This reverts commit 1997e85edc644b700ccd76b33decc933d98c4cbe.
Merge branch 'pulls/exception-string-fix' into master