Updated colors to align with the KU Leuven Visual Identity Guidelines

[LaurensS]

This replaces the default blueXIIlight and blueXIIdark colors to ensure they are consistent with the color scheme defined in the guidelines (https://www.kuleuven.be/communicatie/marketing/en/intranet/branding/downloads/huisstijlhandboek-eng.pdf) and cover template color (https://set.kuleuven.be/phd/researchers/template_kaft/templatephd-ads.docx). It also provides a number of additional accent colors that can be used in the text:

• kullightblue and kulcorporateblue: the colors from the kuleuven logo
• kulprimaryblue, kulsecondaryblue, kultertiarylightblue, kultertiaryblue, kultertiarydarkblue: blue accent colors
• kultertiaryaccent[1-12]: the other (non-blue) accent colors as shown in the visual identity guidelines