Improvement of Visualize Loss, backup the loss list and create a new node without validation

[stephanbrunker]

Within this PR are three commits:

• 1cc2554 improves the Visualize Loss function. If you save states, the loss is not saved too. So when the occasional crashes happen, you lose the loss plot which is quite useful in determining which epoch to pick. So I saved the loss list to the states folder. Then, the shift because of the running average in the loss plot was not considered, the plot is now shifted for the window_size to the right. I also saved a list of savepoints with the states and marked these savepoints with vertical lines in the plot that you can see where exactly your savepoints are.
• 51aa87f simply changes the epoch in the progress bar to the total number if you resume from a saved state.
• 785bc6d adds a new loop node without validation. Validation gets an OOM when training with 16GB VRAM. So this node is a copy of the normal loop node, without validation. I also made the prompt input to the init node optional to create a cleaner workflow.