[Feature Request] Show Maintenance Status

[brandoningli]

It doesn't appear that the sensors take Maintenance into account at all. Binary Sensors show Disconnected, and the regular sensors show a state of "up". My proposal is to:

• Have a configurable option on whether to consider a binary sensor up during maintenance. I'd prefer it to be up, but others may prefer it down
• Update the (regular) sensor states to properly reflect maintenance. States should ideally be "Up", "Maintenance", and "Down".
• Any available maintenance parameters provided by the API for each monitor (type, end time, title, description, etc.) should be presented as attributes.