Change to datetime objects

[tsyesika]

Currently in the internals of MegBot we typically use unix timestamps retrieved by time.time however I think we should start using datetime objects they make it so much easier to do so many things. There places which will need changing will be:

• IRCObjects (Helper.HumanTime, Helper.TimeZoneCorrect)
• dent plugin
• ddate plugin (unsure)
• weather plugin
• seen plugin