[fix] new_issue.html: drop inline style attributes (CSP conformance)

Inline styles are blocked by default with Content Security Policy (CSP).  Move
the inline styles from 'new_issue.html' to::

    searx/static/themes/__common__/less/new_issue.less

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/static/themes/simple/less/style.less

@@ -6,6 +6,8 @@
 
 @stacked-bar-chart: rgb(0, 0, 0);
 
+@import "../../__common__/less/new_issue.less";
+
 @import "normalize.less";
 
 @import "definitions.less";