Make allowedHours const

[ahnolds]

• [x] This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• [x] I have thoroughly tested my contribution.
• [x] Should this code require changes to documentation I will contribute those to https://github.com/ThingPulse/docs.

Right now allowedHours/setAllowedHours take a plain unsigned char pointer. The allowedHours array is never modified, so it would be beneficial to have it be const so that a caller can pass in a const array without having to cast away the const.

[marcelstoer]

Thanks. I'm sure we have a ton of variables that could be made constants or use smaller data types than what they currently use.