Fix plugins commands

Change platforms property of IPlugin from string[] to Server.DevicePlatform[] type. Add try-catch when fetching data for specific plugin - this way if we fail while fetching data for one of the plugins, information about rest of them will be shown to user.

Change url to MarketPlace to use https instead of http.

Fixes http://teampulse.telerik.com/view#item/280934
http://teampulse.telerik.com/view#item/280394
Thanks, you are great :) 
Timeout option is not suitable as the idea here is just to skip the plugins which are not available at the moment, but to give some information, that they exist, so you can use them when everything works fine on our side (the issue occurs when a new plugin is published and there is some strange period when we have information that such plugin exists, but we cannot get details for it).