Fix #71 study lifetime 7 days.

- this is a hard one to test, but doable if we really want to.
- secondary cleanup by update path in the AddonUpdater (to eventual version 99, depends on Gregg and Ilana)
- 7 days currenlty, hard-set
reasons const added
Merge branch 'master' of github.com:raymak/contextualfeaturerecommender
conflict resolved
selfuninstaller merge