make: add application name to bin folder structure

This adds the application name as a subdir to the bin folder hierarchy.
For one this is similar to how packages are build and also will allow
for out-of-source builds of multiple applications.

Makefile.include

@@ -17,7 +17,7 @@ GITCACHE       ?= $(RIOTTOOLS)/git/git-cache
 APPDIR         ?= $(CURDIR)
 BUILDOUT_DIR   ?= $(APPDIR)/build
 BINDIRBASE     ?= $(BUILDOUT_DIR)/bin
-BINDIR         ?= $(BINDIRBASE)/$(BOARD)
+BINDIR         ?= $(BINDIRBASE)/$(BOARD)/$(APPLICATION)
 PKGDIRBASE     ?= $(BUILDOUT_DIR)/pkg/$(BOARD)
 DLCACHE        ?= $(RIOTTOOLS)/dlcache/dlcache.sh
 DLCACHE_DIR    ?= $(RIOTBASE)/.dlcache