make copyright headers more consistent
"The Bitcoin developers" and "The Bitcoin Core developers" is the
dominant use. Fix the few occurences of "Developers" (capital D).
Remove one occurence of a "-" between the authors and the year, and one extra "-" after the first year.
Replace "Bitcoin developers" with "The Bitcoin developers" in one file.
$./contrib/devtools/copyright_header.py report . 34 with unexpected copyright holder names
$./contrib/devtools/copyright_header.py report . 27 with unexpected copyright holder names
Reviewers: #bitcoin_abc, majcosta
Reviewed By: #bitcoin_abc, majcosta
Differential Revision: https://reviews.bitcoinabc.org/D9816