Merge pull request #810 from ddurnev/agents

[RJA-1789][fix]: allow user to create instances only if at least one environment is accessible
[RJA-1790] [fix] - Rest returns error code 500 instead of 403
Merge pull request #811 from rsvato/agents

[RJA-1790] [fix] - Rest returns error code 500 instead of 403
[RJA-1669][feature] introducing metrics first steps
Merge branch 'fb-remoting' of github.com:griddynamics/OpenGenesis into fb-remoting
Merge pull request #812 from bugzmanov/fb-remoting

[RJA-1669][feature] introducing metrics first steps
[RJA-xxx] fixing failed build
Merge pull request #813 from bugzmanov/fb-remoting

[RJA-xxx] fixing failed build
[RJA-1792][fix]: email notification plugin should not send authentication in case of username is empty.