Add functionality to erase devices in FindMyiPhone

[lynatic1337]

Breaking change

This PR is based on #227 and therefore has all changes this PR has. Otherwise no breaking changes. I saw it as necessary to base my PR on this PR to reduce the risk of accidentally erasing family devices.

Proposed change

• add function erase_device in AppleDevice class that takes an eraseToken for specified device and erases that device using it.
• add function fmipWebAuthenticate in PyiCloudService that requests such a token from Apple for a device
• add property canWipe to AppleDevice. This property specifies whether a device supports remote erasion

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New service (thank you!)
• New feature (which adds functionality to an existing service)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests
• Documentation or code sample

Example of code:

Usage example:
This code loops through all your devices and prompts you to erase the first one that supports remote erasion

api.find_my_iphone.with_family = False
api.find_my_iphone.refresh_client()

for x in range(0,len(api.find_my_iphone.devices)):
    currentDevice = api.find_my_iphone.device(x)
    print("Device", currentDevice.name, "does support remote erasure: ", currentDevice.canWipe)
    if (currentDevice.canWipe):
        erasetoken = api.fmipWebAuthenticate(currentDevice)
        print(erasetoken)
        input("Submit anything to wipe device")
        currentDevice.erase_device(text="",erasetoken=erasetoken)
        break

Additional information

• This PR fixes issue: implements proposal from RemoteWipe using findMyiPhone Library #341

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated to README