Add GitHub autobuild

[pmconrad]

Part of bitshares/bitshares-core#2054

Adds auto-build triggers for push and pr using Github's new "Actions" feature. Effects can be seen in my personal repo: https://github.com/pmconrad/fc/actions

[oxarbitrage]

Is there a place where we can check the github build before merging into master ?

https://github.com/bitshares/bitshares-fc/actions?query=branch%3Amaster will redirect to new action and https://github.com/bitshares/bitshares-fc/actions?query=branch%3A2054_github_autobuild the same.

sorry, i overlooked the OP. Link here https://github.com/pmconrad/fc/actions