Introduce relationships as first-class objects (#607)

* migrate pkg.ID and pkg.Relationship to artifact package

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* return relationships from tasks

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* fix more tests

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add artifact.Identifiable by Identity() method

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* fix linting

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* remove catalog ID assignment

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* adjust spdx helpers to use copy of packages

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* stabilize package ID relative to encode-decode format cycles

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* rename Identity() to ID()

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* use zero value for nils in ID generation

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* enable source.Location to be identifiable

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* hoist up package relationship discovery to analysis stage

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* update ownership-by-file-overlap relationship description

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add test reminders to put new relationships under test

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* adjust PHP composer.lock parser function to return relationships

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

internal/presenter/poweruser/json_presenter_test.go

@@ -33,7 +33,6 @@ func TestJSONPresenter(t *testing.T) {
 	catalog := pkg.NewCatalog()
 
 	catalog.Add(pkg.Package{
-		ID:      "package-1-id",
 		Name:    "package-1",
 		Version: "1.0.1",
 		Locations: []source.Location{
@@ -57,7 +56,6 @@ func TestJSONPresenter(t *testing.T) {
 		},
 	})
 	catalog.Add(pkg.Package{
-		ID:      "package-2-id",
 		Name:    "package-2",
 		Version: "2.0.1",
 		Locations: []source.Location{

internal/presenter/poweruser/test-fixtures/snapshot/TestJSONPresenter.golden

@@ -72,7 +72,7 @@
  ],
  "artifacts": [
   {
-   "id": "package-1-id",
+   "id": "b84dfe0eb2c5670f",
    "name": "package-1",
    "version": "1.0.1",
    "type": "python",
@@ -102,7 +102,7 @@
    }
   },
   {
-   "id": "package-2-id",
+   "id": "6619226d6979963f",
    "name": "package-2",
    "version": "2.0.1",
    "type": "deb",