Introduced a PgAdmin class inherited from the Flask, which looks for

submodules inherited from the PgAdminModule instead of regular
Blueprint. This allows us to load the module automatically from the
under the pgadmin directory, and will work to extend the pgAdmin
extension module.

PgAdminModule is inherited from the Blueprint, and bring several
methods:
-  get_own_stylesheets, which returns the stylesheets used by the module
   (excluding its submodules stylesheets)
- get_own_javascripts
- menu_items, which returns a dictionray mapping the old hook names
  (context_items etc) to a list of MenuItem instances

For more specialized modules (as for now, any module that should be part
of the browser tree construction), one can define an abstract base class
defining additional methods.

For example, the BrowserPluginModule abstract base class defines the
following methods:
- jssnippets
- csssnipeets
- node_type
- get_nodes

web/pgadmin/utils/__init__.py

@@ -0,0 +1,80 @@
+from flask import Blueprint
+from collections import defaultdict
+from operator import attrgetter
+import sys
+
+
+
+class PgAdminModule(Blueprint):
+    """
+    Base class for every PgAdmin Module.
+
+    This class defines a set of method and attributes that
+    every module should implement.
+    """
+
+    def __init__(self, name, import_name, **kwargs):
+        kwargs.setdefault('url_prefix', '/' + name)
+        kwargs.setdefault('template_folder', 'templates')
+        kwargs.setdefault('static_folder', 'static')
+        self.submodules = []
+        super(PgAdminModule, self).__init__(name, import_name, **kwargs)
+
+    def register(self, app, options, first_registration=False):
+        """
+        Override the default register function to automagically register
+        sub-modules at once.
+        """
+        if first_registration:
+            self.submodules = list(app.find_submodules(self.import_name))
+        super(PgAdminModule, self).register(app, options, first_registration)
+        for module in self.submodules:
+            app.register_blueprint(module)
+
+    def get_own_stylesheets(self):
+        """
+        Returns:
+            list: the stylesheets used by this module, not including any
+                stylesheet needed by the submodules.
+        """
+        return []
+
+    def get_own_javascripts(self):
+        """
+        Returns:
+            list: the javascripts used by this module, not including
+                any script needed by the submodules.
+        """
+        return []
+
+    def get_own_menuitems(self):
+        """
+        Returns:
+            dict: the menuitems for this module, not including
+                any needed from the submodules.
+        """
+        return defaultdict(list)
+
+    @property
+    def stylesheets(self):
+        stylesheets = self.get_own_stylesheets()
+        for module in self.submodules:
+            stylesheets.extend(module.stylesheets)
+        return stylesheets
+
+    @property
+    def javascripts(self):
+        javascripts = self.get_own_javascripts()
+        for module in self.submodules:
+            javascripts.extend(module.javascripts)
+        return javascripts
+
+    @property
+    def menu_items(self):
+        menu_items = self.get_own_menuitems()
+        for module in self.submodules:
+            for key, value in module.menu_items.items():
+                menu_items[key].extend(value)
+        menu_items = {key: sorted(values, key=attrgetter('priority'))
+                      for key, values in menu_items.items()}
+        return menu_items

web/pgadmin/utils/menu.py

@@ -0,0 +1,6 @@
+from collections import namedtuple
+
+class MenuItem(object):
+
+    def __init__(self, **kwargs):
+        self.__dict__.update(**kwargs)