#652 - add button to clear font color (go back to automatic appropriate color)

...in/java/de/deadlocker8/budgetmaster/icon/IconService.java

src/main/resources/languages/base_de.properties

src/main/resources/languages/base_en.properties

src/main/resources/static/css/style.css

src/main/resources/static/js/categories.js

src/main/resources/static/js/fontColorPicker.js

src/main/resources/static/js/main.js

src/main/resources/templates/categories/newCategory.ftl