Ability to disable bundled apps

[1000TurquoisePogs]

This enhancement allows you to put the following in your YAML

components:
  tn3270-ng2:
    enabled: false

If you did that prior, nothing much would happen. No errors, but no benefit.
Now, this is respected.

The logic is a bit silly:

1. startup checks if the /plugins folder needs to be reset and add back all bundled and core plugins based on if core plugins are there
2. extensions and non-bundled plugins are added or removed from /plugins folder depending upon "enabled" status of yaml
3. NEW - bundled plugins are REMOVED if the YAML has them marked disabled

So, 1) adds them blindly, and 3) removes them conditionally. Kind of silly but I did not want to cause any backward compatibility issues or update the "defaults" folder.

Defaults are unchanged. This just allows you to customize which plugins are available.

In this PR I also spotted a bug about manifest.json not being handled.
I have never seen a manifest.json. They have always been manifest.yaml
But during v2.0 development, we said it would be possible and so this code was written but untested I guess.

[timgerstel]

lgtm

[timgerstel]

now properly searches Zowe share folder for components like the ones in system-apps