* Mega build script improvements

* Look for project.clj to determine root directory since we delete .git on CI for speed

* If .git folder is missing (i.e., in CI) fail gracefully

* Don't need to generate version file to run Cypress tests, right?

* Build uberjar step can cache version.properties
(so the Cypress test steps don't need to generate it again)

* Flush caches

* Update uberjar cache key