update plot displayed datetime to LOCAL rather than UTC times

[Keegan-Evans]

Currently the plots on the dashboard display datetimes in UTC. This is clearly not the most desirable, but arises from the fact that Dash and Plotly upon which the dashboard is built upon squash any datetimes into UTC, at least(seemingly) in the versions compatible with the currently available pandas libraries(at time of issue creation, latest available for Raspberry Pi is 1.5.3; not sure if pandas is the real blocker, it also kind of seems like it is just a dash/plotly implementation issue). This appears to be a consistently requested feature for dash/plotly, and there seems to be some work towards implementing it, though as of now there is not a clear cut solution available that will work on the current sensor-hub platform.

When a newer version of pandas is available(or someone spends the time getting it to build reliably for Raspberry Pi, I have spent quite a bit of time trying to make this work) this might change, so keeping up-to-date on both pandas and dash/plotly releases to determine when it might be possible to implement. Currently there do seem to be some "hacky" solutions available, but they are not straightforward to implement or very robust seeming.

most promising discussion/progress
historic/seemingly current dev position as stated on old, but currently open issue
additional discussion #1