Añade componente para crear menús

También introduce el nuevo módulo Admin para porporcionar un entorno
común de administración para los demás módulos de PageTop.

src/base/component/block.rs

@@ -0,0 +1,105 @@
+use crate::prelude::*;
+
+pub struct Block {
+    renderable: fn() -> bool,
+    weight    : i8,
+    id        : Option<String>,
+    title     : String,
+    markup    : Vec<Markup>,
+    template  : String,
+}
+
+impl PageComponent for Block {
+
+    fn prepare() -> Self {
+        Block {
+            renderable: always,
+            weight    : 0,
+            id        : None,
+            title     : "".to_string(),
+            markup    : Vec::new(),
+            template  : "default".to_string(),
+        }
+    }
+
+    fn is_renderable(&self) -> bool {
+        (self.renderable)()
+    }
+
+    fn weight(&self) -> i8 {
+        self.weight
+    }
+
+    fn default_render(&self, assets: &mut PageAssets) -> Markup {
+        let id = assets.required_id(self.name(), self.id());
+        html! {
+            div id=(id) class="block" {
+                @if !self.title.is_empty() {
+                    h2 class="block-title" { (self.title) }
+                }
+                div class="block-body" {
+                    @for markup in self.markup.iter() {
+                        (*markup)
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl Block {
+
+    pub fn markup(markup: Markup) -> Self {
+        Block::prepare().add_markup(markup)
+    }
+
+    // Block BUILDER.
+
+    pub fn with_renderable(mut self, renderable: fn() -> bool) -> Self {
+        self.renderable = renderable;
+        self
+    }
+
+    pub fn with_weight(mut self, weight: i8) -> Self {
+        self.weight = weight;
+        self
+    }
+
+    pub fn with_id(mut self, id: &str) -> Self {
+        self.id = util::valid_id(id);
+        self
+    }
+
+    pub fn with_title(mut self, title: &str) -> Self {
+        self.title = title.to_string();
+        self
+    }
+
+    pub fn add_markup(mut self, markup: Markup) -> Self {
+        self.markup.push(markup);
+        self
+    }
+
+    pub fn using_template(mut self, template: &str) -> Self {
+        self.template = template.to_string();
+        self
+    }
+
+    // Block GETTERS.
+
+    pub fn id(&self) -> &str {
+        util::assigned_value(&self.id)
+    }
+
+    pub fn title(&self) -> &str {
+        self.title.as_str()
+    }
+
+    pub fn template(&self) -> &str {
+        self.template.as_str()
+    }
+}
+
+fn always() -> bool {
+    true
+}