Numerous improvement to the seeder's code

Summary:

• unsigned char => uint8_t
• C++ style imprts
• project import before library imports
• Relocate some comments for better layout
• Reorder inline and static qualifiers
• Remove blanket namespace imports
• Upgrade some of the loops for C++11 style loops

Test Plan: Compile and run the seeder.

Reviewers: sickpig, schancel, dagurval, freetrader, #bitcoin_abc

Reviewed By: sickpig, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D560