zsh and bash tab-completions

Adds files into ' master/contrib/' and 'slave/contrib' that can be used to enable tab-completion in zsh/bash.

Zsh completion files are the standard twisted wrapper files, copied from twisted/python/twisted-completion.zsh. These files uses functionality in twisted to generate completions.

Bash completion files are regular completions files, which does not use twisted. They provide basic completion implementation, compared to zsh. Currently twisted does not support generating completions for bash.

Also added some completions hints to Options classes to improve completion suggestions in zsh.