Improvements to topic list

[craicoverflow]

The "Retention" column should specify that this is retention in milliseconds, otherwise we could try and make it match exactly that of the UI (relative time).

[craicoverflow]

When the retention period is -1, we should instead show "Unlimited" in the column.

[rkpattnaik780]

Should this be done for retention size as well?

[craicoverflow]

Yeah I think it should.