Add support for tracking parcels shipped with Cainiao

[sam-jeffery]

I've been missing the ability to track Cainiao (Aliexpress) parcels on this app which held me off from deleting my other parcel tracking app, so thought I'd have a look at adding it. Turns out it isn't that difficult!

Summary of changes:

• Added new delivery service for Cainiao deliveries in CainiaoDeliveryService.kt
• Added it to the Services enum and getDeliveryService in Core.kt
• Added a new status for when items have cleared customs but not left it yet. I don't know if you've already decided against this before so happy to remove it if you want but though I'd add it as it's a bit more clear than just 'In transit'.
• Updated readme to include Cainiao as a supported service.

I couldn't come up with any tests for this one as it seems that the tracking number can take a few formats based on the local delivery service used when the parcel arrives in the destination country, and I only have a few tracking numbers to test with from my own parcels. It will detect invalid codes in the app just fine by checking it with the API, though.

I gathered together any status codes I could find from my tracking codes and what I could find on the Aliexpress subreddit, I think most of them are covered but there may be a few uncommon ones that I didn't get. Its a bit difficult since there is no documentation for this api.

Main parcels list:

Package in transit:

Delivered package:

Invalid tracking code:

Let me know what you think, happy to make any changes :)

[itsvic-dev]

lgtm. this was already WIP in #24 but im glad to finally have a finished, more up-to-date implementation.