Feature custom sidecar 1123 (#1129)

* Working on custom sidecar, #1123

* Working on custom sidecar, #1123

* Added custom sidecar example

* Added WRITE_SKIPPED argument for --sidecar-template

* Updated report writer for user sidecars

* Added noqa to long lines in report writer

* Initial tests for --sidecar-template

* Initial tests for --sidecar-template

* Initial tests for --sidecar-template

* Completed tests for --sidecar-template

* Added json example for --sidecar-template

* Added json example for --sidecar-template

examples/custom_sidecar_json.mako

@@ -0,0 +1,6 @@
+<%doc>
+Mako template to dump a full json representation of the photo object
+Can be run from the command line with:
+osxphotos export /path/to/export --sidecar-template custom_sidecar_json.mako "{filepath}.json" yes no yes
+</%doc>
+${photo.json(shallow=False, indent=4)}