Introduce ProviderOptions class

It is a template class for provider's options, it inherits from OptionsPage.

picard/coverart/providers/__init__.py

@@ -19,13 +19,51 @@
 
 from picard import log, config
 from picard.plugin import ExtensionPoint
+from picard.ui.options import OptionsPage, register_options_page
 
 
 _cover_art_providers = ExtensionPoint()
 
 
+class ProviderOptions(OptionsPage):
+
+    """ Template class for provider's options
+
+        It works like OptionsPage for the most (options, load, save)
+        It will append the provider's options page as a child of the main
+        cover art's options page.
+
+        The property _options_ui must be set to a valid Qt Ui class
+        containing the layout and widgets for defined provider's options.
+
+        A specific provider class (inhereting from CoverArtProvider) has
+        to set the subclassed ProviderOptions as OPTIONS property.
+        Options will be registered at the same time as the provider.
+
+        class MyProviderOptions(ProviderOptions):
+            _options_ui = Ui_MyProviderOptions
+            ....
+
+        class MyProvider(CoverArtProvider):
+            OPTIONS = ProviderOptionsMyProvider
+            ....
+
+    """
+
+    PARENT = "cover"
+
+    def __init__(self, parent=None):
+        super(ProviderOptions, self).__init__(parent)
+        self.ui = self._options_ui()
+        self.ui.setupUi(self)
+
+
 def register_cover_art_provider(provider):
     _cover_art_providers.register(provider.__module__, provider)
+    if hasattr(provider, 'OPTIONS') and provider.OPTIONS:
+        provider.OPTIONS.NAME = provider.NAME
+        provider.OPTIONS.TITLE = provider.TITLE or provider.NAME
+        register_options_page(provider.OPTIONS)
 
 
 def cover_art_providers():