Patch komodo checkpoint fix check fork

[dimxy]

Refactored komodo_checkpoint and komodo_get_last_block_time as dedicated function, fixed komodo_check_fork_is_valid so finds a branch with nota not assuming nota always in the best chain

[dimxy]

I also rebased the original patch-komodo-checkpoint that's why it's so many commits

[dimxy]

adds a fix to #10 (fix komodo_check_fork_is_valid function so it does not assume that a nota exists in the best chain)

[dimxy]

see also this https://github.com/KomodoPlatform/zebra/issues/10#issuecomment-1476782527

[dimxy]

included in #45