Superblock (de)serialization using internal mechanisms.

[denravonska]

We currently use a homebrew, Gridcoin specific format for superblocks which mix tagged syntax with binary data. This format is cumbersome to use and it does not leverage existing serialization mechanisms.

We should replace all the contents in Pack/UnpackBinarySuperblock with serialization of classes using the functions in serialize.h. This has several benefits:

• Less code
• More readable
• Easier to maintain
• Faster
• Builtin endian handling
• Smaller contracts

This may be a future issue as it changes the format of the superblocks and will require a mandatory.

[denravonska]

Moved to main repo.