ENH: improve bash completion functionality (issue #551)
- use complete -o filenames, dropped -o nospace to make it more responsive. - restructure completion code to use a unified backend, which makes it easier understand, maintain and re-use. - foamCreateBashCompletions now simply outputs to a stdout, and allows quick generation of completion of single applications. - add -fileHandler completion in anticipation of future changes there. - relocated as etc/config.s/bash_completion to prevent inadvertently having two versions (.com, .org) installed at the same time.