renamed Src folder to ScreamMain
- Src will cause confusion with the addition of plugins
- ScreamMain will define the entry point for the executable
created skeleton for integrating plugins and template plugin
- some black magic to create a common entry point for all plugins
- easy to add create new plugins, simply add the name to list of plugins
  to init and tick. would be nice to have concepts so we can enforce
  some rules
- cmakelists is still a little unclean. creating a new plugin requires
  some amount of hacking the cmakelists. maybe write a script to
  automate the process?