More user-editable CSS-Styles for Custom Layout

Introduction

Right now you can do basic styling operations for the white labeled Cloud-hosted version of Xibo via the admin Interface or by overwriting the Style in the CSS file of the Theme. The Possibilities are very limited but sufficient in most cases.

User Story

Trying to apply a slightly different Style (actually just a few color changes) i´ve noticed, that you can change the Text-Color for the Hover-State of the horizontal main navigation, but you can´t change the color for the Normal-State. Changing the border-bottom color of the navigation items or removing it at all would also be nice. I would like to plead in general for more powers and customization possibilities for the override.css