Handle relative perceived effort (RPE) workouts

[bdlangton]

Hi, thanks so much for this product! It's saved me so much time.

One issue that I ran into is that I have a lot of workouts in TrainingPeaks that are RPE based. When those get copied to Intervals, the workout gets copied but no steps get copied (in the description I just see the Imported with tp2intervals text).

I know RPE is kind of difficult to handle and Intervals doesn't really fully support it. But I've found that even if it doesn't show a nice graph of effort levels or anything, I'd still like the workout structure (intervals, warmup, cooldown, etc) to show up and to show text as to what RPE levels to expect. I've made some quick updates to try and resolve this (I'll make a PR).