Minor test work, no functional changes.

* node-cache: return refs instead of clone for speed.
* add '--disableDbCaching' flag
* reduce heap usage by 50% (118MB -> 58.8MB via Chrome Heap Profiler) via disabling source map during build
* improve generation speed by 75% via SQL query caching

Using full-th sample app as reference, there are 108,871 SQL query calls
spread over the following query functions

* selectAtomicType()
* selectBitmapByName()
* selectDataTypeByName()
* selectEnumByName()
* selectNumberByName()
* selectStructByName()

Performance metric:
  test runner: ./src-script/gen-test-runner.js
  machine: macbook 2.6 Ghz 6-core Intel Core i7 / 32GB DDR4

  Before:
    average generation time: 42.851s

  After:
    initial cache warm up generation time: 17.699s
    average generation time: 11.766s

* fix Nexus asset query issue.

was not constructing continuationToken URL correctly.

* ignore temp artifact files.

* unit test for download-artifact

* update cached download-artifact.js

* ignore download-artifact test from zap unit tests.

* download-artifact: add unit test / delegate to Github if specified branch is not cached on Nexus

intended for internal jenkins PRs that specifies a non-cached ZAP branch
on Nexus

* typescript
* do not check for github token when downloading from Nexus

* instrument codebase via babel-plugin-istanbul for Cypress
* direct jest report to jest-coverage / cypress report to cypress-coverage 
* combine/display code coverage report from all tests via "npm run report"

BUG:  ZAPP-774

0. Enshrine privilege as an alias for role.
1. Update some script that was path sensitive.
2. Ignore generated package file.