quizzes/git: Add 'git status' question
ui.cli: Don't start the QuestionCommandLine with an empty stack

There's not much point in a question-answering shell if there are no
questions to be answered.
quizzes/git: Add 'git commit -a' question
quizzes/git: Avoid escaped double-quotes when single-quotes will do
quizzes/git: Add 'git diff *' questions

New questions:
* git diff
* git diff HEAD --
* git diff HEAD -- README
* git diff --cached
quizzes/git: Add 'git log *' questions

New questions:
* git log
* git log -p
* git log --stat
* git log --all
* git log --oneline
* git log --oneline --graph
* git log --oneline --decorate
quizzes/git: Add 'git rm / commit' question
quizzes/git: Fix 'in repository' -> 'in your repository'

For the 'git rm / commit' question.
quizzes/git: Add 'git branch *' questions

New questions:
* git branch
* git branch -a
* git branch -r
* git branch -d
quizzes/git: Add 'git checkout *' questions

New questions:
* git checkout
* git checkout -b
* git checkout -b NEW_BRANCH START_POINT
quizzer/git: Add 'git merge' question
quizzes/git: Add remote-related questions

New questions:
* git remote add
* git remote -v
* git fetch REPOSITORY
* git push REPOSITORY BRANCH