`treehouses editor` (fixes #1440)

[darthnoward]

fixes #1440 commands to set environment variable EDITOR and configure text editors

root@treehouses:~/cli# ./cli.sh editor 

Error: default editor not set.
Use "treehouses editor default"
or "treehouses editor set [vim|emacs|nano]" to set your default editor.

root@treehouses:~/cli# ./cli.sh editor set nano
Text editor is now nano.

root@treehouses:~/cli# ./cli.sh editor
nano

root@treehouses:~/cli# ./cli.sh editor default
Text editor is now vim, using the default config.

using config from a file

root@treehouses:~/cli# echo "set number" > ~/vimrc

root@treehouses:~/cli# ./cli.sh editor config ~/vimrc
vim is now using config from file "/root/vimrc".

reset config to default

root@treehouses:~/cli# ./cli.sh editor config default
vim config reset to default.

sections involving emacs is not yet implemented as emacs isn't included in builder yet