I need to create a library for WP 8+ Apps that will recognize touches and gestures (and storing info about that). Is there a way to do this using Portable Class Library?
Yes. You can include Windows.Phone.Controls
(in my case from C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v8.1\Libraries
) since it is supported on a PCL with the Windows Phone 8.1
subset.