Fixes #838 Entity transform timezone

**Fix Time.parse timezone issue**

By default, Ruby parses string times to the system timezone, if the string doesn't contain timezone information. This is problematic, since time is stored to MySQL in UTC, without timezone information. Thus it should be parsed to UTC, not to system's timezone.

**Disable ActiveRecord timezone awareness**

The timezone was set to Helsinki, which is obviously wrong. We don't want to make Active Record to use Helsinki timezone, instead, in the future, we might want to make Active Record aware of user's timezone.
utc_time_to_str name would describe the transformer functionality better