Implement email content transformation according Content-Transfer-Encoding header

[mixas27]

Implement email content transformation according Content-Transfer-Encoding header

[ctapobep]

@jk1 will you have time to implement this in Pochta? Currently we need only base64 transformation.

Pochta may have a separate JSON field with "body as is" and "user friendly body" or it may use content type from HTTP Request it gets from REST client in order to determine in what form it should spit out the content.

[jk1]

@ctapobep, sure

[jk1]

So I've added some basic decoder to show a mail in a pseudo-rendered readable form. Mail JSON now contains both rendered and raw mail versions. Never tested it on really complex samples though)

@mixas27, @ctapobep please let me know if current implementation suits your needs