Naming inconsistencies and potential improvements

[sarusso]

To dig in:

• series.autodetected_sampling_interval vs series.resolution vs series.sampling_interval
• plot(height) vs plot(max_y) vs plot(y_range)

Naming conventions at the moment:

• timestamp (time stamp not present at all)
• timezone (time zone not present at all)
• time series (timeseries only in code and some comments)
• data point / datapoint (mixed, fix it)

Check also:

• series.tz vs series.as_timezone()
• storage series_type, maybe move to items_type?

Clarify indexes data vs key-value data etc.