Add CSS class to categories to allow custom styling

doc/de_DE/individuel-category.markdown

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+Inviduelle Kategorien Darstellung
+=================================
+
+
+
+Setup
+-----
+
+1: Einstellung > Anwendungskonfiguration > benutzerdefiniertes Stylesheet
+
+Für den Kategorien-Container allgemeine Darstellung
+```css
+.task-board-category-container-color span {
+  border: solid 0.5px grey;
+  color: black;
+}
+```
+
+Für den Text-Inhalt
+```css
+[class*="category-Patchkanditat"] {
+  background-color: rgba(255, 0, 0, 0.50);
+  border: none!important;
+  font-weight: bold;
+  font-style: italic;
+  box-shadow: 0 1px 1px rgba(186, 186, 186, 0.55);
+  color: white!important;
+  font-size:11px;
+}
+```
+![CAT](./screenshots/kanboard_patch_category.PNG)

doc/en_US/individuel-category.markdown

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+Individual category markup
+===========================
+
+
+Setup
+-----
+
+1: Settings > Application settings > Custom Stylesheet
+
+For the category container:
+```css
+.task-board-category-container-color span {
+  border: solid 0.5px grey;
+  color: black;
+}
+
+```
+Custom css values for one category - this is an example for displaying the text: 
+```css
+[class*="category-Patchkanditat"] {
+  background-color: rgba(255, 0, 0, 0.50);
+  border: none!important;
+  font-weight: bold;
+  font-style: italic;
+  box-shadow: 0 1px 1px rgba(186, 186, 186, 0.55);
+  color: white!important;
+  font-size:11px;
+}
+```
+![CAT](../de_DE/screenshots/kanboard_patch_category.PNG)