cppcheck: upgrade to 1.67
Merge pull request #391 from toxeus/upgradeCppCheck

cppcheck: upgrade to 1.67
OTCheque: rename class to Cheque
OTCheque: rename files to Cheque.{h,c}pp
Merge pull request #387 from toxeus/develop

OTCheque: rename to Cheque
UserCmdGetBoxReceipt: remove unused parameter
UserCmdGetBoxReceipt: remove commented out condition
Merge pull request #397 from toxeus/develop

UserCmdGetBoxReceipt: remove confusions
Use SendMessage() call

OT still has some remnants of a SSL connection system that was removed in favor
of ZeroMQ. The OTServerConnection class does a lot of stuff that may have made
sense earlier but can be removed and simplified now.

This is the first step of a larger cleanup.

The old code had this repeated pattern

m_pClient->SetFocusToServerAndNym(*pServer, *pNym, m_pTransportCallback);
m_pClient->ProcessMessageOut(theMessage);
return m_pClient->CalcReturnVal(lRequestNumber);

and a variant that does not have last call to CalcReturnVal()

I replaced these two variants two atomic methods

* SendMessage(OTServerContract*, OTPseudonym*, OTMessage&, lRequestNumber)
* SendMessage(OTServerContract*, OTPseudonym*, OTmessage&)

The other place where SetFocusToServerAndNym is called now is in opentxs-script
which I will do separately.
Merge pull request #395 from OttoAllmendinger/pr-otapi-sendmessage

Use SendMessage() call
Some small comment cleanups
Remove -2 as an error code

The error code is never checked.

The methods for handling the error are not implemented.

The error is unlikely to occur.

The error can be prevented by using the correct data types.