*: add code to serialize templates into go code

Add a small program to iterate over the templates directory and
generate a go map of name to file data. This is so we can compile
these templates into the dex binary instead of requiring files on
disk.

Also add a Makefile rule to do this automatically.

Makefile

@@ -19,7 +19,7 @@ GOARCH=$(shell go env GOARCH)
 
 build: bin/dex bin/example-app
 
-bin/dex: FORCE
+bin/dex: FORCE server/templates_default.go
 	@go install -ldflags $(LD_FLAGS) $(REPO_PATH)/cmd/dex
 
 bin/example-app: FORCE
@@ -42,6 +42,9 @@ lint:
       golint $$package; \
 	done
 
+server/templates_default.go: $(wildcard web/templates/**)
+	@go run server/templates_default_gen.go
+
 .PHONY: docker-build
 docker-build: bin/dex
 	@docker build -t $(DOCKER_IMAGE) .