GUI2: allow labels to shrink to avoid scrollbars

This adds a new can_shrink key to widgets that allows the 'no label' codepath of styled_widget::request_reduce_width to be called.
In this case, it allows labels to shrink without forcing window scrollbars.

data/gui/schema.cfg

@@ -481,6 +481,11 @@
                         type="unsigned"
                         default=0
                     [/key]
+                    [key]
+                        name="can_shrink"
+                        type="bool"
+                        default=false
+                    [/key]
                     [tag]
                         name="linked_group"
                         min="0"

data/gui/widget/label_default.cfg

@@ -20,6 +20,8 @@
 		max_width = 0
 		max_height = 0
 
+		can_shrink = true
+
 		text_font_family = {FONT_FAMILY}
 		text_font_size = {FONT_SIZE}
 		text_font_style = {FONT_STYLE}

src/gui/core/widget_definition.cpp

@@ -98,6 +98,7 @@ resolution_definition::resolution_definition(const config& cfg)
 	, default_height(cfg["default_height"])
 	, max_width(cfg["max_width"])
 	, max_height(cfg["max_height"])
+	, can_shrink(cfg["can_shrink"].to_bool())
 	, linked_groups()
 	, text_extra_width(cfg["text_extra_width"])
 	, text_extra_height(cfg["text_extra_height"])

src/gui/core/widget_definition.hpp

@@ -57,6 +57,8 @@ struct resolution_definition
 	unsigned max_width;
 	unsigned max_height;
 
+	bool can_shrink;
+
 	std::vector<linked_group_definition> linked_groups;
 
 	unsigned text_extra_width;

src/gui/widgets/styled_widget.cpp

@@ -219,7 +219,7 @@ void styled_widget::request_reduce_width(const unsigned maximum_width)
 				  << "' maximum_width " << maximum_width << " result " << size
 				  << ".\n";
 
-	} else if(label_.empty()) {
+	} else if(label_.empty() || config_->can_shrink) {
 		point size = get_best_size();
 		point min_size = get_config_minimum_size();
 		size.x = std::min(size.x, std::max<int>(maximum_width, min_size.x));