Added update_interval to maxcube

[dingusdk]

Description:

Fixes the "reset to factory issue" with maxcube. (see this forum post:
https://community.home-assistant.io/t/maxcube-loosing-configuration/46663/11)

I have added an "update_interval" configuration parameter. Having a longer update interval fixes the issue

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#5265

Example entry for configuration.yaml (if applicable):

maxcube:
  gateways:
    - host: 192.168.0.20
      update_interval: 300

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code communicates with devices, web services, or third-party tools:

• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[OttoWinter]

This should be a cv.time_period and preferably also cv.positive_timedelta.

vol.All(cv.time_period, cv.positive_timedelta)

[dingusdk]

I have changed it to cv.time_period, and convert to total seconds (I did not make the original max cube code, and wanted to make as few changes as possible, and the original code has the update interval in seconds - hard coded to 60 seconds)

[OttoWinter]

I'm not sure about this configuration key name. Most platforms use scan_interval for an update/scan interval.

IMO update_interval makes more sense, but scan_interval would be much more consistent.

[dingusdk]

I have changed it to scan_interval to be more consistent