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.
The tricky part is, they aren't that separate.
When I wrote this I thought a bit ahead of how I wanted Download Clients/Notifications to work.
I figured that we would start filing in some default values for certain fields, without actually adding it to the constructor of the settings.
Instead you would add a DefaultDefinition and set the defaults there.
Newznab has a default without a name, but Wombles has a default with a name. I imagine someone would do the same for notifications, after all, it's unlikely you have two plex servers to notify.
This could potentially replace the Enable/OnGrab/OnDownload that is currently in the UI code.