[Qt] make PaymentServer::ipcParseCommandLine void

- the function only returned true, so make it void
- add a comment about payment request network detection
[Qt] add BIP70/BIP71 constants for all messages and mime types

- also rename current ones to match the new ones
- remove constant from guiconstant.h and add it to paymentserver.cpp
[Qt] ensure socket is set to NULL in PaymentServer::ipcSendCommandLine
[Qt] remove dup lock that is done in SetAddressBook()
[Qt] add BIP70 payment request size DoS protection for URIs

- current code only does this for payment request files, which are
  used on Mac
- also rename readPaymentRequest to readPaymentRequestFromFile, so it's
  obvious that function only handles payment request files and not URIs
- small logging changes in readPaymentRequestFromFile
[Qt] add BIP70 DoS protection test

- this test required to make readPaymentRequestFromFile() public in order
  to be able to is it in paymentservertests.cpp
[Qt] update paymentserver license and cleanup ordering
Merge pull request #5216

5ec654b [Qt] update paymentserver license and cleanup ordering (Philip Kaufmann)
4333e26 [Qt] add BIP70 DoS protection test (Philip Kaufmann)
31f8494 [Qt] add BIP70 payment request size DoS protection for URIs (Philip Kaufmann)
2284ccb [Qt] remove dup lock that is done in SetAddressBook() (Philip Kaufmann)
1ec753f [Qt] ensure socket is set to NULL in PaymentServer::ipcSendCommandLine (Philip Kaufmann)
814429d [Qt] add BIP70/BIP71 constants for all messages and mime types (Philip Kaufmann)
b82695b [Qt] make PaymentServer::ipcParseCommandLine void (Philip Kaufmann)