Add overview in Competencies page

[MakisH]

Adds an improvised Table of Contents. Making this automatically is not particularly easy.

Alternative, hard-coded overview (that I made before I check how easy it is):

## Overview

- Software engineering skills
  - [Creating documented code building blocks (DOCBB)](#DOCBB)
  - [Building distributable libraries (LIBS)](#LIBS)
  - [Adapting to the software life-cycle (SWLC)](#SWLC)
  - [Use repositories (SWREPOS)](#SWREPOS)
  - [Software behaviour awareness and analysis (MOD)](#MOD)
- Rsearch skills
  - [Curiosity (NEW)](#NEW)
  - [Understanding the research cycle (RC)](#RC)
  - [Software re-use (SRU)](#SRU)
  - [Software publication (SP)](#SP)
  - [Using domain repositories/directories (DOMREP)](#DOMREP)
- Communication skills
  - [Working in a team (TEAM)](#TEAM)
  - [Teaching (TEACH)](#TEACH)
  - [Project management (PM)](#PM)
  - [Interaction with users and other stakeholders (USERS)](#USERS)

The difference is that the hard-coded one uses the skill codes as bookmarks.

@jpthiele FYI