move from chrono to time crate

[LesnyRumcajs]

Summary of changes
Changes introduced in this pull request:

• move from chrono to time crate to resolve RUSTSEC-2020-0071 and RUSTSEC-2020-0159 in Remove Cargo Audit Ignores #1247
• remove direct usage of chrono crate in the project

[LesnyRumcajs]

Vulnerable time 0.1.43 is still present as chrono exists in few other dependencies (or rather dependencies of dependencies). Will look into this later, but seems we may need to do changes in other crates to get rid of the issue.