- they where useing date_between instead of date_between_inclusion

^

use advanced instead of duration, as it is more timezone safe

fix and make tests with Time more explicit and timezone safe

fix format helper test

fix format helper test

remove tz_parse helper

- volunteer got all hours and feedbacks belonging to all volunteers in the
  group offer displayed
- scoped relation on group_assignment to hours and feedbacks wasn't utilized in
  hours_since_last_submitted and feedbacks_since_last_submitted methods

- so that they are not billable
- billing expenses are imported seperately, and that legacy source table
  doesn't carry relations to the hour records in the legacy db

- relations include deleted now
- hours have correct import record attributes now, to be findable

- deduplicating features between existing trial feedbacks list.
- merging common things into concerns

...be calculated automaticly before_validation

- Presuming Assignment Types (kinds)
- build values inside certificate model before save
- adapt hours model to accept 0 ours if there is minutes
- volunteer model delivers hash with assignment kinds it has
- volunteers table boolean fields have default false, so messy catching
  of boolean field with nil value is not neccesary anymore