Release v0.12.8 Download Related Fixes

What's Changed

• ST-932 go routine to TransferSendMessageToPPServ() by @WangLiStratos in #733
• fix/ST-938 fix backup failure by @WangLiStratos in #734
• ST-933_572 detailed error messages in rpc api, download error handling by @WangLiStratos in #735
• Release v0.12.8 by @alexstratos in #737
• fix/ST-979 check failure handler before use it by @WangLiStratos in #738
• Release v0.12.8-b by @alexstratos in #739

Full Changelog: v0.12.7...v0.12.8