Listing images panics

[HarryMichal]

Podman changed their JSON API again causing Toolbox to panic when listing images (toolbox list -i or simply toolbox list). The affected field of the JSON is Created that used to hold a string with a human-readable representation of time (e.g., 5 minutes ago). That field was changed to an int (but the Go code sees it as a float) with UNIX time.

Before the discussion in the mentioned PR comes to some result, Toolbox should be overall more resilient when some change in the API happens.

Output of toolbox --version:

toolbox version 0.0.92

Output of podman version:

Version:      2.1.0-dev
API Version:  1
Go Version:   go1.14.3
Built:        Thu Jan  1 01:00:00 1970
OS/Arch:      linux/amd64