* Added support for --plugin parameter in Fission CLI
This fixes the issue that renaming fission to fission-XYZ would cause a fork bomb, due to the CLI recursively calling itself to discover plugins.
This PR introduces extensibility to the Fission CLI. The principle behind the design of this extensibility is taken from the approach git uses: the main binary (fission) calls other binaries (fission-workflows) - which it discovers using simple prefix-rules - based on specific commands (fission workflow <command>).