Support for PC flattening, autoflatten on levelup, flatten options

[shun17]

Hi, I made some modifications vor v11 months ago, but I wasn't able to submit a pull request.

I made some modifications to enhance the NPCs and PCs flattening, using the same sulf for all bonuses to prevent problem during flatten/unlfatten, using also the official sulggifier of pf2e system. I also made selectable the rounding mode and added button for flatten/unflatten all actors.

I saw that the functionality for PCs was removed, but I used it a lot in my campagin, so still worth workin on it for me, so I'm suibmitting the pull request with the functionality restored.

If something is wrong or need some clarification feel free to reach me, thanks a lot for the add-on

[velara]

I'm going to have to spend some time thinking about whether I want to implement this as is or pull some stuff out of it and integrate it in a fashion that's more in line with how I tend to code. There's some features you've implemented that I think are definitely worth adding. But there's several sections that are fairly different from the approach I would take, which means they're harder for me to maintain.

[shun17]

I tried to generalize the code splitting it in "logic section" based on the context:

• the first section for the configuration and the user configuration options
• the registration on init for the gm screen of the various buttons
• all the event hooks logic
• the actual flattening logic for who and how to flatten

Let me know if you need some rework or anything else