Fix bugs + Add improvements to graph

[Ahmed-Khaled-dev]

Bugs:

• Fix bug If I play git commit and then git checkout, and then I try to play any other level, the game sometimes totally freezes or when I enter again the level git commit, the HEAD is standing like it's standing on top of a commit, but at the same time there are no commits visible, and also if I play git commit and then git checkout the last place I check out to is the first commit (the one to the left) and then play git commit again, when I enter git checkout the HEAD will move automatically to the first commit (the left one), while it should be on the latest commit (the right one), so please test this part thoroughly to identify any bugs and fix them

• Git checkout level doesn't show the correct code that i have added in the git commit level for each commit when i checkout

Improvements:

• The new look of the commit message is beautiful but can have some improvements, I think making the shape itself a bit bigger and the font bigger would result in it being easier to read and also the text and the shape are a bit blurry, so if this can be fixed somehow using setSmooth or something else
• Make the checkout level relation with the edit window contents and the commit names to be more educational, so at the start, it should show the contents of the latest commit, not "type here", and commit names should resemble the content in the code of each commit, to make the player better understand the idea
• Make the idea of an arrow that shows which branch I am currently on like in Git branching game or OhMyGit (But then take care, you would need to adjust the HEAD functionality a bit, for it to stand on the branch name itself, since this is actually what happens in git, (HEAD -> main) by default if you remember, that's why it always moves with it when we create new commits) (This feature will be necessary for creating a git branching level)
  Example:
  
• Make the commits numbered like In git branching (Or make their number pop up when I hover over them)
  Example: