I2CDevices: Add SHT3x temperature humidity sensor

[t-mon]

nymea-plugins pull request checklist:

• [x] Make sure the pull request's title is of format "Plugin name: Add support for xyz" or "New plugin: Plugin name"

• [ ] Did you test the changes on hardware, if not (e.g. absence of required hardware), please mention a person to confirm it has been tested.

• [x] Did you update the plugin's README.md accordingly?

• [x] Did you update translations (cd builddir && make lupdate)?

• [x] If you added a new plugin, should it be added to nymea-plugins-all or nymea-plugins-maker?

[nymea-jenkins]

Refer to this link for build results (access rights to CI server needed): https://jenkins.nymea.io/job/nymea-plugins-pull-request-tester/1626/

[mzanetti]

Mind completing the checklist so I can rebase another branch for this plugin on top please

[t-mon]

Done, I still need to test it, but should be fine to use as base.

[nymea-jenkins]

Refer to this link for build results (access rights to CI server needed): https://jenkins.nymea.io/job/nymea-plugins-pull-request-tester/1721/

[nymea-jenkins]

Refer to this link for build results (access rights to CI server needed): https://jenkins.nymea.io/job/nymea-plugins-pull-request-tester/1722/

[mzanetti]

Untagging as a conflicting branch is subject to land in 0.30