Added an update to pull assetgroups and use proxy

Added the following updates:

• Added the ability to configure the http, socks4 or socks5 proxy via the splunk default Proxy setting features in Splunk add-on builder
• Added the ability to pull assetgroups and its subdomains/assets into a new sourcetype.
• Better handling of any API errors encountered, to ensure that API calls will be repeated
• Added extra options to control the number of pages downloaded and back-off timers in case of errors.
• Converted Assetnote instance field from normal text to password text field.