Add style property to barfi.st_barfi

[GsLogiMaker]

This pull request implements the custom styling that I requested in #24.

Below is an example of whats possible with this feature:

Source

node = bf.Block("Block")
node.add_input("In")
node.add_output("Out")
node.add_option("Data", "input")

bf.st_barfi(
	[node],
	style="""
	.button-menu {
		visibility: hidden;
	}
	.node {
		visibility: hidden;
	}
	.node > .__title {
		visibility: visible;
	}
	.node > .__content {
            background: red;
		border-radius: 0px 0px 32px 32px;
		visibility: visible;
        }
	.node-editor > .background {
		background: green;
	}
	""",
)

Result

And of course you could make it look really good if you tried.