Add is_online property

[codecov[bot]]

Codecov Report

Base: 65.08% // Head: 65.21% // Increases project coverage by +0.13% :tada:

Coverage data is based on head (47a6433) compared to base (f6c447d). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #36 +/- ## ========================================== + Coverage 65.08% 65.21% +0.13% ========================================== Files 6 6 Lines 799 802 +3 ========================================== + Hits 520 523 +3 Misses 279 279 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `65.21% <100.00%> (+0.13%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=J.+Nick+Koston#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/bdraco/nexia/pull/36?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=J.+Nick+Koston) | Coverage Δ | | |---|---|---| | [nexia/thermostat.py](https://codecov.io/gh/bdraco/nexia/pull/36/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=J.+Nick+Koston#diff-bmV4aWEvdGhlcm1vc3RhdC5weQ==) | `69.29% <100.00%> (+0.36%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=J.+Nick+Koston). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=J.+Nick+Koston)

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