Added Presets to Indexers

The logic also exists for DownloadClients and Notifications, but they don't show coz there aren't any default definitions.
Also added a Info Link button linking to the wiki pages.

Please pay special attention to the SchemaBuilder change, I effectively use the preset to copy any default values that don't have a FieldDefinition, so anything that doesn't get sent to the UI.
It seems weird to separate the first item from the rest of them, if they are the same. While I can see how they are all just templates (blank or filled in), handling them differently feels awkward,

2 plex servers to notify might be unlikely, but multiple XBMC machines would be expected (I have 3 setup in drone).