Is your feature request related to a problem? Please describe.
The problem with the current state of scripts is that they don't support cross-platform flawlessly. Writing a shell script under Linux that helps setting up my python project won't do it on Windows.

Describe the solution you'd like
We should replace these platform dependent scripts with platform independent Lua scripts. Lua is capable of running shell commands too and those scripts would be executable on all platforms. These scripts will from now on be called plugins.
Additionally we should create a central repo where we host trusted scripts; a repo like for example proji-official-plugins. Plugins will behave just like scripts did until now.