CB-5647 Move <assets> copying from install to prepare

This is for cordova-cli to remove .staging.
GitHub: close #53
CB-6076 Log message tweaks.
CB-5006 Add a cache in searchpath logic.

Sped up CCA: 5.3 -> 5.0 seconds.
CB-6115 Updated version and RELEASENOTES.md for release 0.20.0
CB-6115 Incremented plugin version to -dev branch.
CB-6122 Fix exception on uninstall due to incorrect require() path.

github: close #55
CB-6123 Fix crash in handleUninstall introduces by recent action-stack refactoring

github: close #56