Add mechanism for bundling UI assets. (#153)

* Add mechanism for bundling UI assets.

The scripts/uigen.sh script will check out the UI repo, build assets,
create a static assets file, and clean up.

The dev Makefile target has been modified to run this script if no
assets file is found. There is also a build-ui target that will
unilaterally update (the dev target only builds if the file isn't found,
but doesn't update).

The handler has been updated to add the default org ID as a header if
the request path is "/".

Co-authored-by: Randall Morey <randall@randallmorey.com>

tools/tools.go

@@ -22,6 +22,7 @@ package tools
 //go:generate go install golang.org/x/tools/cmd/goimports
 //go:generate go install github.com/oligot/go-mod-upgrade
 //go:generate go install github.com/mitchellh/gox
+//go:generate go install github.com/go-bindata/go-bindata/v3/go-bindata
 
 import (
 	_ "github.com/bufbuild/buf/cmd/buf"
@@ -44,4 +45,6 @@ import (
 	_ "github.com/oligot/go-mod-upgrade"
 
 	_ "github.com/mitchellh/gox"
+
+	_ "github.com/go-bindata/go-bindata/v3/go-bindata"
 )