Add additional alert properties about weatheralerts

[jlverhagen]

I've got a pull request started here: #29

that adds those additional properties. It also allows zone or county ID number to be specified and later today I'll push a commit that adds PlatformNotReady to allow the component to retry the setup if weather.gov request fails during the first setup try.

[jlverhagen]

The latest release of weatheralerts contains several additional alert properties. The full list:

sensor attribute	alert property
area	areaDesc
certainty	certainty
description	description
ends	ends
event	event
instruction	instruction
response	response
sent	sent
severity	severity
title	headline (everything before ' by ')
urgency	urgency
NWSheadline	parameters:NWSheadline
effective	effective
expires	expires
onset	onset
status	status
messageType	messageType
category	category
sender	sender
senderName	senderName
id	id
zoneid	feedid (passed to alert api URL)

I kept 'area' instead of renaming it to 'areaDesc' so it wouldn't break any existing configurations. I changed 'title' to add the issued date and time. If that isn't desired, 'event' can be used instead of 'title'. The 'zoneid' is set to equal the full 6 character zone ID or a comma separated list of the 6 character zone and county ID's that are passed to the weather.gov alert api URL.

I didn't think any of the other alert properties were particularly useful. If you disagree, feel free to comment on which additional properties you think would be useful and I'll get them in there.

[stale]

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