Add an implementation to reset (clean) individual files/directories

[Smolations]

I have run into issues every now and then when random modified/untracked files show up in my working tree after a java build or some other action. It spurned this feature request. There are two issues I'd like this implementation to address:

1. git checkout [treeish] -- <path/to/fileOrDirectory
   • This is necessary when wanting to grab a version of a file/directory and pull it into the current working tree. It would be nice to have bash_completion on this feature to complete file paths and [treeish] commits.
2. git clean [-f | --force] [-d] [-n | --dry-run]
   • It would be nice to have a menu pop up which allows a user to choose specific modified/untracked files/directories to clean, as well as the option to clean all.
   • A nice-to-have feature would be the option to see changes in modified files using some variation of git diff as well as an option to open files/folders in a text editor (if the user configures a default editor).