Butterfly should be configurable via an external configuration file

[fabiocarvalho777]

Butterfly should be configurable via an external configuration file. Requirements:

1. This file format should be either properties or yaml (research pros and cons of both and decide the best option)
2. This file should be named .butterfly and placed under $HOME/, similar to .gitconfig for example.
3. The properties to be configurable should be classified as:
   1. Global properties: Butterfly properties independent from the extension to be run
   2. Extension specific properties: properties defined and used by installed extensions
4. A few examples of global properties:
   1. Toggle to turn metrics ON (true) or OFF (false). If ON, at least one metrics jar would have to be present to have metrics generated. Default to false.
   2. Toggle to stop upgrades (true) if an upgrade step has produced manual instructions. That would give a chance for the user to complete the manual instructions, and then, run Butterfly again, to continue the upgrade from that point. If off, the upgrade continues all to the end and all generated post-transformation manual instructions are collected and reported in the end. Default to false.
5. Global and extension properties can be overridden by setting the property as a CLI option parameter.

Update end user documentation accordingly.