prompt: added clover theme

Please pull this branch into sorin-ionescu/master.

This branch add a prompt theme with configurable colors (either 4 or 8 colors). The does works as expected minus the first loding with prompt... it requires sourcing it in ~/.zshrc first. It works as expected afterwards. Even with numerous theme switching.

I cannot found the origin of this issue. BRACE_CCL is problematic with this theme. Maybe a LOCAL_OPTIONS should be added first to avoid a conflict with environment module.