split off osmo-mgw: remove files, apply build, rename

Add vty and logging previously used from libcommon

Rename libmgcp to libosmo-legacy-mgcp and install.

Use DLMGCP, not DMGCP.

Slim down the public mgcpgw_client API, move all elements not actually used by
current callers to private headers / static c.

Depends: libosmocore I09c587e2d59472cbde852d467d457254746d9e67
Change-Id: I71a0a16ebaaef881c34235849601fc40aa12cfd7
diff --git a/include/osmocom/Makefile.am b/include/osmocom/Makefile.am
new file mode 100644
index 0000000..6514436
--- /dev/null
+++ b/include/osmocom/Makefile.am
@@ -0,0 +1,3 @@
+SUBDIRS = \
+	legacy_mgcp \
+	$(NULL)