Add store for dapps state (#3211)

* Add mobx

* Use mobx store for dapps

* Cleanup hidden reads

* Remove (now) unused hidden.js

* _ denotes internal functions

* s/visibleApps/visible/

* AddDapps now use the mobx store as well

* Move modalOpen state to store

* Simplify

* Complete master merge

* Remove extra indirection

* Remove unneeded check

* Readability improvements

* Remove final debug info