Fix schedule ending at midnight and wrong rain status if plugin started when wet

[mookkari]

Fixes:

• When the schedule ended at midnight ("endAt": "24:00:00") UpdateFromMqtt changed 24:00 to 00:00 meaning that the date's schedule was removed in the next set_schedule call.
• rainStatusCode will be read in InitValues. If the plugin was initialized when it is wet it was showing default status value "Dry" until the rain status was updated from mqtt. It seems like Mqtt will update the rain status only when it is changed, so it might take hours (or days?) to get the correct status when it's raining for a long time.
• Modified documentation with examples of schedule ending at midnight.