refactor: Create chaintype files

This is the first of a number of commits with the goal of moving the
chain type definitions out of chainparamsbase to their own file and
implementing them as enums instead of constant strings. The goal is to
allow the kernel chainparams to no longer include chainparamsbase.

The commit is part of an ongoing effort to decouple the libbitcoinkernel
library from the ArgsManager and other functionality that should not be
part of the kernel library.

src/Makefile.am

@@ -280,6 +280,7 @@ BITCOIN_CORE_H = \
   util/bip32.h \
   util/bitdeque.h \
   util/bytevectorhash.h \
+  util/chaintype.h \
   util/check.h \
   util/epochguard.h \
   util/error.h \
@@ -707,6 +708,7 @@ libbitcoin_util_a_SOURCES = \
   util/asmap.cpp \
   util/bip32.cpp \
   util/bytevectorhash.cpp \
+  util/chaintype.cpp \
   util/check.cpp \
   util/error.cpp \
   util/exception.cpp \
@@ -956,6 +958,7 @@ libbitcoinkernel_la_SOURCES = \
   txdb.cpp \
   txmempool.cpp \
   uint256.cpp \
+  util/chaintype.cpp \
   util/check.cpp \
   util/exception.cpp \
   util/fs.cpp \