DiffEditor should have a button "reload"

• DiffEditor is opened from the Commit dialog
• You inspect the chunks and want to change something
• Double click leads to an Editor where the changes are made
• You save and go back to DiffEditor and like to see the new changes

Current Situation:

• Close DiffEditor
• Change to the Commit Window
• Open DiffEditor again

Expected Situation:

• Choose a menu item or button "Reload" in DiffEditor which does the same