cppcheck: remove unused functions

Unused functions removed:
    SetupHeader()
    OTClientConnection::AddToOutputList()
    OTClientConnection::GetNextInputMessage()
    OTClientConnection::GetNextOutputMessage()
    OTClientConnection::ProcessBuffer()
    OTServer::VerifyBasketAccountID()

Functions removed in consequence:
    OTClientConnection::ReadBytesIntoBuffer()
    OTClientConnection::ProcessMessage()
    OTClientConnection::ProcessType1Cmd()
    OTClientConnection::AddToInputList()
OTClientConnection: remove declaration of unimplemented method
Merge pull request #63 from toxeus/removeUnusedFunction

Remove unused functions
cppcheck: upgrade to 1.66
Merge pull request #64 from toxeus/updateCppcheck

cppcheck: upgrade to 1.66
remove /*=NULL*/ comments

Command used:
    sed -r -i 's|/\*=NULL\*/||g' "$file"
remove /*=<SOMETHING>*/ comments

Command used:
    sed -r -i 's|/\*=[^ ]+\*/||g' "$file"
remove this-> pointer usage

Command used:
    sed -r -i 's/this->//g' "$file"
Merge pull request #65 from toxeus/removeClutter

Remove clutter
use nullptr instead of NULL

Command used:
    sed -r -i 's/([^[:alpha:]])NULL([^[:alpha:]]|$)/\1nullptr\2/g' "$file"
Merge pull request #66 from toxeus/removeNULL

use nullptr instead of NULL
ServerLoader: remove ZMQ2 artifacts