Detect Differences Between Two Commits Feature

• Add two GtkEntry objects that accepts the commits hashes as input
• Add a new GtkButton Object to issue the detecting command
• Add a new GtkTextView Object to preview the difference between the two commits
• Retrieve Commits Objects from the user inputted SHAs to be compared
• Retrieve Diff Object using Diff.tree_to_tree() method, and figure out how to extract diff data on the Gtk.TextView

Fixes #1 (closed)