v1.5.4b1

Changes taken from upstream/CHANGELOG.md

• send correct/default OpenConnect's User-Agent string (openconnect#245)
• allow unset certificate/key from CertStore (openconnect#131)
• VPN protocol selection on quick profile setup dialog
• don't forget to set all default vpn profile settings on quick connect setup
• dynamically load VPN protocol list; add GlobalProtect protocol (openconnect#158)

Other changes

• Qt upgraded to 5.15 (better support to osx dark mode)
• Hide App from Dock (osx)