Auto-update live demo server with Checker Framework major update.

[CharlesZ-Chen]

It is a tedious and annoying procedure to require maintainer update live demo server each time when there is a major update of CF.

Implement an auto update feature would eliminate this annoying manual procedure.

Technically, this could be done easily (maybe as an URA project for second year undergrads). Here is a draft idea about how to implement it:

1. Change typetools/CF travis file, so that: if this is a commit of a major version update (could be recognize by git --tag argument), trigger an update.sh in eisop sever.

2. Then the update.sh will fetch the updated version of CF.

3. To auto-update available checkers and their examples, following jobs is required:
   3.1 Decoupling the hard code of the list of checkers and examples in front end html.
   3.2 Record checker list and examples in a file with some standard data format (yaml maybe a good option) (ideally, this file should be add into CF, and it is CF responsibility to maintain this file).
   3.3 Dynamically generate the checker lists and example links by injecting the data in the file described in 3.2.