[Feature] Add proxy options to plugin define

This allows to make use of a Proxy server for installation of plugins.
This will work for http and https sites.
Update readme for proxy feature
Merge pull request #162 from electrical/master

[TESTING] Fix correct package version
Merge pull request #163 from electrical/master

[TESTING] more fixes for correct version
Merge pull request #164 from electrical/master

[TESTING] Forgot 2 more version numbers
Merge pull request #158 from electrical/plugin_proxy

[Feature] Add proxy options to plugin define
Merge pull request #167 from electrical/master

Fix Instance define