Llama2c WASM UI improvements (#732)

* pass seed, expose model seq_len

* wip new llama2.c ui

* final new UI example

* small coppy

* copy

candle-wasm-examples/llama2-c/src/worker.rs

@@ -51,7 +51,7 @@ fn read_tensor<R: std::io::Read, S: Into<Shape>>(
 
 pub struct Model {
     pub cache: Cache,
-    config: Config,
+    pub config: Config,
     pub llama: Llama,
     pub tokenizer: Tokenizer,
 }