Cancellation policy per host

[keang]

Currently each supplier implementation hard codes the cancellation policy that is parsed.
We need to add the ability for each host to customise the cancellation policy, because the multi-host suppliers may have contracts that dictate different policies for different hosts.

Solution

• Add a field in the host edit/create page, where we can choose from a dropdown
• Show the cancellation policy on hosts index page.
• Update each suppliers implementations to read cancellation policy from host