More functions in webui, interface is more adapted to mobile

[CORRUPTOR2037]

New functions:

• changing color for session
• add italic and bold text support
• left and right columns can be hidden
• regenerate message (any or last)
• continue generation
• delete message function now deletes not only selected message, but also everything below
• input field locked to the bottom of the screen

[turboderp]

I'll have to take some time to look this over, but I'm not a fan of this bit:

delete message function now deletes not only selected message, but also everything below

It's one of the features I rely on for testing.

And regenerating messages has always been possible by just deleting and pressing enter (?). But I'll give it a look.

The web UI needs to be refactored a bunch before it should be expanded too much, I think. It really is written in large parts by GPT-4 and very much in spite of me. As cool as GPT-4 is, it isn't exactly consistent with its methodology or coding style.