[ISSUE-434] Increase charge cost scale / kWh

[baylanger]

@adriankumpf - I had a few things to fix on my Mac, all done and got my dev env up & running.

Before making my changes, I added a geo-fence location with a cost price of 0.05

I made my changes and the database modify automatically reflected the adjustment from "0.05" to "0.0500".

 id | name | latitude | longitude | radius |     inserted_at     |     updated_at      | cost_per_kwh
----+------+----------+-----------+--------+---------------------+---------------------+--------------
  1 | test |        0 |         0 |     20 | 2020-02-12 06:12:17 | 2020-02-12 06:12:17 |       0.0500

I was required to adjust some values in test/teslamate/log/log_charging_test.exs - I'm no Exilir pro, ... please double check my changes.

[adriankumpf]

Well done. Thank you!