feat: Add multi-user profiles to mirror character profiles

[q5sys]

I sometimes want a different 'persona' for my own user depending on the other character I'm going to be chatting with. But since the UI only had one default character with a single name and field, I would have to keep a text file and copy/paste all the details about the user I was going to be for the chat.

But a while ago I started to get annoyed by doing that change everytime, so I patched this locally so I could save variations of 'me' for different chats.

I just updated to the latest release and I figure there's probably others who would like the same functionality, so I decided to file a PR.

I'm happy to make any modifications or changes that you would prefer to what I've written. I tried to follow your existing code style by where possible by re-using existing lines that were close to what I needed and then modifying them as required. Like the Character Saver in ui_file_saving.py where I cloned L29-40 to L42-53 for the User saver and then updated the necessary strings.

But I'm happy to make any changes you want.

Checklist:

• [ X ] I have read the Contributing guidelines.

I ran through all the files I changed with pyflakes and pycodestyle. No output from either linter.

[q5@apollo modules]$ pyflakes shared.py 
[q5@apollo modules]$ pyflakes utils.py
[q5@apollo modules]$ pyflakes chat.py
[q5@apollo modules]$ pyflakes ui_chat.py
[q5@apollo modules]$ pyflakes ui_file_saving.py 
[q5@apollo modules]$ pyflakes ui.py
[q5@apollo modules]$ pycodestyle shared.py 
[q5@apollo modules]$ pycodestyle utils.py 
[q5@apollo modules]$ pycodestyle chat.py 
[q5@apollo modules]$ pycodestyle ui_chat.py 
[q5@apollo modules]$ pycodestyle ui_file_saving.py 
[q5@apollo modules]$ pycodestyle ui.py
[q5@apollo modules]$ 

[oobabooga]

Thanks for the PR! The implementation is very clean and integrates well with the existing code. I made just a few minor improvements. Merging now.