Cleanup the confusion between the various platform objects

[itziakos]

There are several platform objects EPDPlatform, LegacyEPDPlatform and Platform. The objects do not really hold the same Information and It is not clear when each object should be used. Even worse the code converts between them by first converting to strings which in most cases results in loss of information.

[itziakos]

• LegacyEDPlatform should be removed
• EPDPlatform should be a set of functions and factories that holds information based on historical Platforms that we have used at Enthought so far. This is to be used for special usecases only.
• Platform should be the instance that should be used by all downstream tools

[itziakos]

#452 remove the use of the LegacyEPDPlatform from the okonomiyaki code (the LegacyEPDPlatform is still available)

[itziakos]

#458 removes the legacy module

[itziakos]

It looks that we cannot tottaly remove the use of EPDPlatform without updating the egg metadata. The code in EPDPlatform is there to guess the Platform instance based on the limited information in our egg metadata.