Remove tabs UI from code editor and move to plugin. Enhance plugin system.

- Remove tabs controller, tab widget, and tabs widget files and move to plugin
- Delete plugins/README.txt
- Add register_controller method to controller system for plugin use
- Add error handling for plugin crashes via futures callback

plugins/code/tabs_bar/plugin.py

@@ -0,0 +1,32 @@
+# Python imports
+
+# Lib imports
+
+# Application imports
+from libs.event_factory import Event_Factory, Code_Event_Types
+
+from plugins.plugin_types import PluginCode
+
+from .tabs_controller import TabsController
+
+
+
+class Plugin(PluginCode):
+    def __init__(self):
+        super(Plugin, self).__init__()
+
+
+    def _controller_message(self, event: Code_Event_Types.CodeEvent):
+            ...
+
+    def load(self):
+        tabs_controller = TabsController()
+        code_container  = self.requests_ui_element("code-container")
+
+        self.register_controller("tabs", tabs_controller)
+
+        code_container.add( tabs_controller.tabs_widget )
+        code_container.reorder_child(tabs_controller.tabs_widget, 0)
+
+    def run(self):
+        ...