Update domain adaptation in TFBS section (greenelab#734). Closes gree…

…nelab#728.

* Update domain adaptation in TFBS section

* Change line length

* update doi

* Revise domain adaptation

* add missing dot

* Add ENCODE-DREAM summary

* Update transfer learning intro paragraph

* Move TFImpute to separate paragraph

* Add FactorNet intro

need to add factornet citation to tags

* Add TSK

todo: TSK tag

* add Singh2016_tsk  and Quang2017_factor

* Update 04.study.md

Fix missing words

* Fix line issue

* Add Anshul's changes

* Update references

* Split paragraphs

* Add ENCODE-Dream ref and discussion reference

* Split paragraphs

* Grammar

* Formatting and grammar

* Switch to DOI reference

* Remove repeated text

* Add RNA binding sentence