[likelihood_bayes, mix_model] Lecture Improvements and Error Fixes (#504)

* Tom's second edits of June 29

* updates

* update new exercise for lrp and minor update to mix_model

* hide output of the pip install

* Tom's first July 30 eduts if likelihood_bayes lecture

* Tom's July 30 edits of wald_Friedman lecture

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Co-authored-by: thomassargent30 <ts43@nyu.edu>

Author: HumphreyYang