make showing the sidebar resizer configurable and hide by default

core/language/en-GB/ThemeTweaks.multids

@@ -21,6 +21,7 @@ Settings/BackgroundImageSize: Page background image size
 Settings/BackgroundImageSize/Auto: Auto
 Settings/BackgroundImageSize/Cover: Cover
 Settings/BackgroundImageSize/Contain: Contain
+Settings/SidebarResizer: Sidebar resizer
 Metrics: Sizes
 Metrics/FontSize: Font size
 Metrics/LineHeight: Line height

core/ui/PageTemplate/sidebar-resizer.tid

@@ -5,6 +5,8 @@ list-after: $:/core/ui/PageTemplate/story
 \import $:/core/macros/sidebar-resizer
 \whitespace trim
 
+<%if [{$:/themes/tiddlywiki/vanilla/options/sidebarresizer}match[show]] %>
+
 <$eventcatcher tag="div" class="tc-sidebar-resizer-pointerdown-eventcatcher" selector=".tc-sidebar-resizer" matchSelector=".tc-sidebar-resizer" $pointerdown=<<sidebar-resizer-pointerdown-actions>> $pointerup=<<sidebar-resizer-pointercancel-actions>>>
 
 <%if [{$:/state/sidebar}!match[no]] %>
@@ -24,3 +26,5 @@ list-after: $:/core/ui/PageTemplate/story
 <% endif %>
 
 </$eventcatcher>
+
+<% endif %>