Only loading addin files from `ProgramData` folder

[alvpickmans]

Issue

Addin files are only being loaded from the installation folder (usually C:\ProgramData\Autodesk\Revit\Addins\{VERSION}), so files found on %appdata%\Autodesk\Revit\Addins\ are omitted.

Proposed solutions

1. Add folder %appdata%\Autodesk\Revit\Addins\{VERSION} as default extra location to retrieve addin files from, and/or
2. Add optional parameter to define additional location(s?) where addin files can be saved, and at least
3. Specify this behaviour on the documentation (only loading addin files from ProgramData)

[vinnividivicci]

I have an ancient suggestion for how to do part of this: https://github.com/DynamoDS/RevitTestFramework/pull/30 https://github.com/vinnividivicci/RevitTestFramework/pull/1