Support "disabling unrecommended" for bundled plugins

* Extended plugin metadata by new property, only evaluated for bundled
    plugins.
  * Adjusted plugin manager to evaluate new metadata and add
    confirmation dialog with details when attempting to disable such
    a plugin.

src/octoprint/plugin/core.py

@@ -71,6 +71,9 @@ class PluginInfo(object):
 	attr_description = '__plugin_description__'
 	""" Module attribute from which to retrieve the plugin's description. """
 
+	attr_disabling_discouraged = '__plugin_disabling_discouraged__'
+	""" Module attribute from which to retrieve the reason why disabling the plugin is discouraged. Only effective if ``self.bundled`` is True. """
+
 	attr_version = '__plugin_version__'
 	""" Module attribute from which to retrieve the plugin's version. """
 
@@ -294,6 +297,19 @@ class PluginInfo(object):
 		"""
 		return self._get_instance_attribute(self.__class__.attr_description, default=self._description)
 
+	@property
+	def disabling_discouraged(self):
+		"""
+		Reason why disabling of this plugin is discouraged. Only evaluated for bundled plugins! Will be taken from
+		the disabling_discouraged attribute of the plugin module as defined in :attr:`attr_disabling_discouraged` if
+		available. False if unset or plugin not bundled.
+
+		Returns:
+		    str or None: Reason why disabling this plugin is discouraged (only for bundled plugins)
+		"""
+		return self._get_instance_attribute(self.__class__.attr_disabling_discouraged, default=False) if self.bundled \
+			else False
+
 	@property
 	def version(self):
 		"""

src/octoprint/plugins/pluginmanager/__init__.py

@@ -706,6 +706,7 @@ class PluginManagerPlugin(octoprint.plugin.SimpleApiPlugin,
 			key=plugin.key,
 			name=plugin.name,
 			description=plugin.description,
+			disabling_discouraged=gettext(plugin.disabling_discouraged) if plugin.disabling_discouraged else False,
 			author=plugin.author,
 			version=plugin.version,
 			url=plugin.url,

src/octoprint/plugins/pluginmanager/static/js/pluginmanager.js

@@ -360,9 +360,26 @@ $(function() {
                     .done(onSuccess)
                     .fail(onError);
             } else {
-                OctoPrint.plugins.pluginmanager.disable(data.key)
-                    .done(onSuccess)
-                    .fail(onError);
+                var perform = function() {
+                    OctoPrint.plugins.pluginmanager.disable(data.key)
+                        .done(onSuccess)
+                        .fail(onError);
+                };
+
+                if (data.disabling_discouraged) {
+                    var message = _.sprintf(gettext("You are about to disable \"%(name)s\"."), {name: data.name})
+                        + "</p><p>" + data.disabling_discouraged;
+                    showConfirmationDialog({
+                        title: gettext("This is not recommended"),
+                        message: message,
+                        question: gettext("Do you still want to disable it?"),
+                        cancel: gettext("Keep enabled"),
+                        proceed: gettext("Disable anyway"),
+                        onproceed: perform
+                    })
+                } else {
+                    perform();
+                }
             }
         };