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Went through the TODOs, removed a bunch, which are outdated or nothing more than a regular comment, documented a bunch more as actual tickets and made them FIXMEs and unified their structure (`FIXME #TICKETNO DESC` for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/support/src/dispatch.rs

@@ -485,7 +485,7 @@ macro_rules! decl_module {
 		// Workaround for https://github.com/rust-lang/rust/issues/26925 . Remove when sorted.
 		#[derive(Clone, Copy, PartialEq, Eq)]
 		#[cfg_attr(feature = "std", derive(Debug))]
-		// TODO: switching based on std feature is because of an issue in
+		// FIXME: switching based on std feature is because of an issue in
 		// serde-derive for when we attempt to derive `Deserialize` on these types,
 		// in a situation where we've imported `srml_support` as another name.
 		#[cfg(feature = "std")]

substrate/srml/support/src/storage/generator.rs

@@ -194,7 +194,7 @@ pub trait StorageMap<K: codec::Codec, V: codec::Codec> {
 	fn mutate<R, F: FnOnce(&mut Self::Query) -> R, S: Storage>(key: &K, f: F, storage: &S) -> R;
 }
 
-// TODO: Remove this in favour of `decl_storage` macro.
+// FIXME #1466 Remove this in favour of `decl_storage` macro.
 /// Declares strongly-typed wrappers around codec-compatible types in storage.
 #[macro_export]
 macro_rules! storage_items {
@@ -445,7 +445,6 @@ macro_rules! __storage_items_internal {
 			}
 
 			/// Get the key used to put the length field.
-			// TODO: concat macro should accept byte literals.
 			fn len_key() -> $crate::rstd::vec::Vec<u8> {
 				let mut key = $prefix.to_vec();
 				key.extend(b"len");
@@ -513,7 +512,7 @@ macro_rules! __handle_wrap_internal {
 	};
 }
 
-// TODO: revisit this idiom once we get `type`s in `impl`s.
+// FIXME: revisit this idiom once we get `type`s in `impl`s.
 /*impl<T: Trait> Module<T> {
 	type Now = super::Now<T>;
 }*/

substrate/srml/support/src/storage/mod.rs

@@ -24,8 +24,6 @@ use codec::{Codec, Decode, KeyedVec, Input};
 #[macro_use]
 pub mod generator;
 
-// TODO: consider using blake256 to avoid possible preimage attack.
-
 struct IncrementalInput<'a> {
 	key: &'a [u8],
 	pos: usize,