Implement a new system to handle "escape actions"

The new EscapeActions object decide what to do when the user press the
Escape key (such as closing a opened popup or inlined form).

This commit also re-introduced the sidebar current view as a sidebar
component local state.

client/components/main/editor.js

@@ -0,0 +1,66 @@
+var dropdownMenuIsOpened = false;
+
+Template.editor.onRendered(function() {
+  var $textarea = this.$('textarea');
+
+  $textarea.textcomplete([
+    // Emojies
+    {
+      match: /\B:([\-+\w]*)$/,
+      search: function(term, callback) {
+        callback($.map(Emoji.values, function(emoji) {
+          return emoji.indexOf(term) === 0 ? emoji : null;
+        }));
+      },
+      template: function(value) {
+        var image = '<img src="' + Emoji.baseImagePath + value + '.png"></img>';
+        return image + value;
+      },
+      replace: function(value) {
+        return ':' + value + ':';
+      },
+      index: 1
+    },
+
+    // User mentions
+    {
+      match: /\B@(\w*)$/,
+      search: function(term, callback) {
+        var currentBoard = Boards.findOne(Session.get('currentBoard'));
+        callback($.map(currentBoard.members, function(member) {
+          var username = Users.findOne(member.userId).username;
+          return username.indexOf(term) === 0 ? username : null;
+        }));
+      },
+      template: function(value) {
+        return value;
+      },
+      replace: function(username) {
+        return '@' + username + ' ';
+      },
+      index: 1
+    }
+  ]);
+
+  // Since commit d474017 jquery-textComplete automatically closes a potential
+  // opened dropdown menu when the user press Escape. This behavior conflicts
+  // with our EscapeActions system, but it's too complicated and hacky to
+  // monkey-pach textComplete to disable it -- I tried. Instead we listen to
+  // 'open' and 'hide' events, and create a ghost escapeAction when the dropdown
+  // is opened (and rely on textComplete to execute the actual action).
+  $textarea.on({
+    'textComplete:show': function() {
+      dropdownMenuIsOpened = true;
+    },
+    'textComplete:hide': function() {
+      Tracker.afterFlush(function() {
+        dropdownMenuIsOpened = false;
+      });
+    }
+  });
+});
+
+EscapeActions.register(10,
+  function() { return dropdownMenuIsOpened; },
+  function() {}
+);