organize essential APIs into platform, workflow and pkg folders (#337)

Add more logic to the way code is organized.

	/pkg -- library code not directly connected to micromdm
	/mdm -- packages meant for the services devices interract with. The MDM protocol.
	/dep -- DEP API and related packages.
	/platform -- Core APIs the server provides. Commands API, Devices API, queue, pubsub etc.
	/workflow -- Packages/API that build on top of platform. Today that's the webhook package.
		     Depending on what ends up here, the workflow folder might become its own repository.

platform/appstore/appstore.go

@@ -0,0 +1,98 @@
+// package appstore provides an abstraction for uploading files and manifests
+// to a repository.
+package appstore
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/groob/plist"
+	"github.com/pkg/errors"
+
+	"github.com/micromdm/micromdm/mdm/appmanifest"
+)
+
+type AppStore interface {
+	SaveFile(name string, f io.Reader) error
+	Manifest(name string) (*appmanifest.Manifest, error)
+	Apps(name string) (map[string]appmanifest.Manifest, error)
+}
+
+type Repo struct {
+	Path string
+}
+
+func (r *Repo) SaveFile(name string, f io.Reader) error {
+	fname := filepath.Join(r.Path, name)
+	file, err := os.Create(fname)
+	if err != nil {
+		return errors.Wrapf(err, "saving file %s", name)
+	}
+	defer file.Close()
+
+	_, err = io.Copy(file, f)
+	return err
+}
+
+func (r *Repo) Manifest(name string) (*appmanifest.Manifest, error) {
+	manifestName := name
+	if !strings.HasSuffix(name, ".plist") {
+		manifestName = name + ".plist"
+
+	}
+	fname := filepath.Join(r.Path, manifestName)
+	file, err := os.Open(fname)
+	if err != nil {
+		return nil, errors.Wrapf(err, "reading manifest %s", name)
+	}
+	defer file.Close()
+
+	var m appmanifest.Manifest
+	if err := plist.NewDecoder(file).Decode(&m); err != nil {
+		return nil, errors.Wrap(err, "decoding manifest file")
+	}
+
+	return &m, nil
+}
+
+func (r *Repo) Apps(name string) (map[string]appmanifest.Manifest, error) {
+	manifests := make(map[string]appmanifest.Manifest)
+	if name != "" {
+		mf, err := os.Open(filepath.Join(r.Path, name))
+		if err != nil {
+			return nil, err
+		}
+		var m appmanifest.Manifest
+		if err := plist.NewDecoder(mf).Decode(&m); err != nil {
+			return nil, err
+		}
+		manifests[name] = m
+		return manifests, nil
+	}
+
+	files, err := ioutil.ReadDir(r.Path)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, file := range files {
+		manifestName := file.Name()
+		if file.IsDir() || filepath.Ext(manifestName) != ".plist" {
+			continue
+		}
+		mf, err := os.Open(filepath.Join(r.Path, manifestName))
+		if err != nil {
+			return nil, err
+		}
+		var m appmanifest.Manifest
+		if err := plist.NewDecoder(mf).Decode(&m); err != nil {
+			return nil, err
+		}
+		manifests[manifestName] = m
+	}
+
+	return manifests, nil
+}