Add issue templates for Epics, User Stories, User Tasks and Technical Tasks

User-Orientated Requirements: `Epic`s, `User Story`-ies and `User Task`s.

```text
          Epics
            |                        \
    User Story 1         ...     User Story N
/                   \
User Task 1 ... User Task N
```

Technical Tasks: `Technical Task`s.

Design work needed for respective templates.