Allow user to specify location for json-c at configuration time.

configure.ac
PKG_CHECK_MODULES for json-c

backend/Makefile.am
cords/Makefile.am
Use: LIBADD instead of LDFLAGS, "JSONC_FLAGS" and "JSONC_LIBS".
Merge remote-tracking branch 'origin/OnApp' into deps_updated

Conflicts:
	backend/Makefile.am
Merge pull request #22 from compatibleone/onapp/json-c_dependencies

Onapp/json c dependencies