Post 2.x release discursion

[ldotlopez]

Once I fix the database corruption bug I plan to release it as 2.0.0 and start the 3.x series.

In fact, I already start testing the waters in the 'dev' branch to experiment some ideas and digging what causes the database corruption.

Some thing I plan to implement:

• Use UTC-timestamps instead of datetime in HistoricalState
• Auto generated statistics by default (get rid of the mandatory implementation)
• Allow overwrite existing states and statistics with upstream data (overlapping data is currently ignored)
• Reusable methods and services to inject historical data into non-historical sensors