Upgrades should auto-remove older versions

[shyamvalsan]

Currently when I try installing a newer version of netdata.msi it errors out saying netdata is Already installed.

This scenario should be handled by prompting the user if they want to remove existing Netdata versions and proceed with the installation.

[dfpr]

The MSI upgrade process will be fixed soon, meanwhile uninstalling before upgrading is the only possibility, thank you for your feedback.

[cakrit]

Closing in favor of #6