Add a plugin_manager module

As the number of plugin types increases, this will make it easier to load
them all.

Change-Id: Ie9eb31c110ea313062e03cf59a2e3021058254f9
Move the code that reads the global environment

This belongs in the environment module, not the resources package.

Change-Id: I97093cef3a3e6d35bc82df8b8533cff7e5bc6ec9
Merge "Add a plugin_manager module"
Merge "Move the code that reads the global environment"