Elements should not call into the various Printers

[ali1234]

Currently each element has various methods to convert a packet into ANSI, or HTML etc. This prevents feeding codepage information to the conversion process, because packets are not aware of each other. Instead, each Element should have one method to return it's displayable data as teletext bytes, and then the top level Packet object should handle conversion. This will avoid having to pass around a lot of state and reduce the amount of boilerplate code in the Elements.

Needed for #63