refactoring

src/main/resources/templates/about.ftl

src/main/resources/templates/accounts/accounts.ftl

src/main/resources/templates/accounts/newAccount.ftl

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

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

src/main/resources/templates/datePicker.ftl

src/main/resources/templates/emptyPage.ftl

src/main/resources/templates/error/403.ftl

src/main/resources/templates/error/404.ftl

src/main/resources/templates/error/418.ftl

src/main/resources/templates/error/500.ftl

src/main/resources/templates/header.ftl

src/main/resources/templates/index.ftl

src/main/resources/templates/login.ftl

src/main/resources/templates/navbar.ftl

src/main/resources/templates/payments/newPayment.ftl

src/main/resources/templates/payments/payments.ftl

src/main/resources/templates/settings.ftl

src/main/resources/templates/validation.ftl