DRY up a common view pattern

Define a Whisper.View base class that automatically parses and renders
templates and attributes defined by the subclass. This saves us a good
number of lines of code as well as some marginal memory overhead, since
we are no longer saving per-instance copies of template strings.

test/views/whisper_view_test.js

@@ -0,0 +1,34 @@
+describe('Whisper.View', function() {
+  it('renders a template with attributes', function() {
+    var viewClass = Whisper.View.extend({
+      template: '<div>{{ variable }}</div>',
+      attributes: {
+        variable: 'value'
+      }
+    });
+
+    var view = new viewClass();
+    view.render();
+    assert.strictEqual(view.$el.html(), '<div>value</div>');
+  });
+  it('renders a template with no attributes', function() {
+    var viewClass = Whisper.View.extend({
+      template: '<div>static text</div>'
+    });
+
+    var view = new viewClass();
+    view.render();
+    assert.strictEqual(view.$el.html(), '<div>static text</div>');
+  });
+  it('renders a template function with attributes function', function() {
+    var viewClass = Whisper.View.extend({
+      template: function() { return '<div>{{ variable }}</div>'; },
+      attributes: function() {
+        return { variable: 'value' };
+      }
+    });
+    var view = new viewClass();
+    view.render();
+    assert.strictEqual(view.$el.html(), '<div>value</div>');
+  });
+});