Add txrequest module

This adds a new module that defines TxRequestTracker, a data
structure that maintains all information about transaction
requests, and coordinates requests.

Backported from: da3b8fd
                 3c7fe0e
                 fd9a006

Original Author: Pieter Wuille <[email protected]>

Conflicts:
- replaced GenTx with uint256 because no segwit
- used int64_t instead of std::chrono::microseconds per utiltime
- removed wtxid tests

src/Makefile.am

@@ -155,6 +155,7 @@ BITCOIN_CORE_H = \
   torcontrol.h \
   txdb.h \
   txmempool.h \
+  txrequest.h \
   ui_interface.h \
   undo.h \
   util.h \
@@ -220,6 +221,7 @@ libdogecoin_server_a_SOURCES = \
   torcontrol.cpp \
   txdb.cpp \
   txmempool.cpp \
+  txrequest.cpp \
   ui_interface.cpp \
   validation.cpp \
   validationinterface.cpp \

src/Makefile.test.include

@@ -135,6 +135,7 @@ BITCOIN_TESTS =\
   test/testutil.h \
   test/timedata_tests.cpp \
   test/transaction_tests.cpp \
+  test/txrequest_tests.cpp \
   test/txvalidationcache_tests.cpp \
   test/versionbits_tests.cpp \
   test/uint256_tests.cpp \