Add post image upload (#20)

Lands the image upload handlers and picker on master. Questions and replies can attach up to four JPEG, PNG, or WebP photos.

Reviewed-on: #20
Co-authored-by: codegirl-007 <s.raide@gmail.com>

internal/web/server_test.go

@@ -173,6 +173,11 @@ func TestRegisterLoginAsk(t *testing.T) {
 		`id="submit-progress"`,
 		`data-submit-once`,
 		`data-submit-button`,
+		`enctype="multipart/form-data"`,
+		`data-image-picker`,
+		`id="submit-images"`,
+		`accept="image/jpeg,image/png,image/webp"`,
+		`Add up to 4 JPEG, PNG, or WebP images.`,
 	} {
 		if !strings.Contains(rec.Body.String(), want) {
 			t.Fatalf("submit form missing %q: %s", want, rec.Body.String())