Add sentence simplification as pre-processing before SRL

[elliottash]

SRL works better on shorter, simpler sentences. We might improve performance by doing sentence simplification as a pre-processing step.

Two promising approaches:

• https://github.com/Lambda-3/DiscourseSimplification
• https://github.com/serenayj/ABCD-ACL2021

[elliottash]

some sample code for sentence simplication is here:

https://www.dropbox.com/scl/fo/lic5r8pc08z6l88ogwm3q/h?dl=0&rlkey=ovn1svpbjae49jtmyd0exd75i