build: add libbitcoinconsensus files and hook up the lib build

Credit BlueMatt for libbitcoinsonsensus.h/cpp

.gitignore

@@ -45,6 +45,7 @@ src/qt/test/moc*.cpp
 
 .deps
 .dirstamp
+.libs
 .*.swp
 *.*~*
 *.bak
@@ -66,6 +67,10 @@ src/qt/test/moc*.cpp
 *.json.h
 *.raw.h
 
+#libtool object files
+*.lo
+*.la
+
 # Compilation and Qt preprocessor part
 *.qm
 Makefile