#509 - prevent page reload on requesting a chart delete (+ no page reload on modal close)

...a/de/deadlocker8/budgetmaster/charts/ChartController.java

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

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

...in/resources/templates/categories/deleteCategoryModal.ftl

src/main/resources/templates/charts/deleteChartModal.ftl

src/main/resources/templates/charts/manage.ftl

src/main/resources/templates/helpers/header.ftl