Limit transaction queue memory & limit future queue (#6038)

* Remove confusing gas_limit in the pool.

* Change defaults

* Limit transaction queue by memory usage.

* Change defaults to something lower.

* Fix rpc test.

* Fix js issues.

* Renamed block_gas_limit

util/src/cache.rs

@@ -76,4 +76,4 @@ impl<K: Eq + Hash, V: HeapSizeOf> MemoryLruCache<K, V> {
 	pub fn current_size(&self) -> usize {
 		self.cur_size
 	}
-}
+}