Document more TODOs as tickets (#1418)

Went through the TODOs, removed a bunch, which are outdated or nothing more than a regular comment, documented a bunch more as actual tickets and made them FIXMEs and unified their structure (`FIXME #TICKETNO DESC` for local tickets, `FIXME: DESC LINK` for external tickets) for easier in-editor support. Further more remove unnecessary remarks and related old code that I noticed in that instance.

substrate/srml/contract/src/lib.rs

@@ -347,12 +347,8 @@ decl_storage! {
 	}
 }
 
-// TODO: consider storing upper-bound for contract's gas limit in fixed-length runtime
-// code in contract itself and use that.
-
 /// The storage items associated with an account/key.
 ///
-/// TODO: keys should also be able to take AsRef<KeyType> to ensure Vec<u8>s can be passed as &[u8]
 pub(crate) struct StorageOf<T>(rstd::marker::PhantomData<T>);
 impl<T: Trait> StorageDoubleMap for StorageOf<T> {
 	const PREFIX: &'static [u8] = b"con:sto:";

substrate/srml/contract/src/wasm/runtime.rs

@@ -196,8 +196,6 @@ fn write_sandbox_memory<T: Trait>(
 // * AFTER MAKING A CHANGE MAKE SURE TO UPDATE COMPLEXITY.MD *
 // ***********************************************************
 
-// TODO: ext_balance, ext_address, ext_callvalue, etc.
-
 // Define a function `fn init_env<E: Ext>() -> HostFunctionSet<E>` that returns
 // a function set which can be imported by an executed contract.
 define_env!(Env, <E: Ext>,