Add favorite words to long term exercise

[ztefanie]

Is your feature request related to a problem? Please describe.
Should words that are marked as favorites be added to the long term exercise?

Describe the solution you'd like
Add words that have been marked as favorites. Do not remove them, after they are unmarked as favorites
Could be annoying if you add a word to favorites and remove it, but it does not get removed when removing it from favorites

Describe alternatives you've considered
Do not add favorites to long term exercise. Could be annoying if you want to learn words that you found in the search.