add project dependencies

Change-Id: I74b841c024d131013da012539d0842cd108438a8

.gitmodules

+[submodule "dependencies/pjproject"]
+	path = dependencies/pjproject
+	url = https://github.com/savoirfairelinux/pjproject
+[submodule "dependencies/opendht"]
+	path = dependencies/opendht
+	url = https://github.com/savoirfairelinux/opendht
+[submodule "dependencies/restinio"]
+	path = dependencies/restinio
+	url = https://github.com/aberaud/restinio

opendht @ 61f43c6b

+Subproject commit 61f43c6b05db0e0cc644e47a7c1e4c8c78b067c2

pjproject @ 1489db07

+Subproject commit 1489db073be280629e41d387c1c2561f20b0bfb3

restinio @ 6fd08b65

+Subproject commit 6fd08b65f6f15899dd0de3c801f6a5462b811c64