Switch from master branch to Cachet 2.4

Summary:
The master branch doesn't contain the up-to-date code.
It currently lives in the 2.4 branch.

An artisan 'cachet:install' command takes care of installation steps.

Ref T1598.

Test Plan: Run test container on Dwellers

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1598

Differential Revision: https://devcentral.nasqueron.org/D2258