Remove As (#2602)

* Start to remove the `As` bound on `SimpleArtithmetic`

This just introduces standard numeric bounds, assuming a minimum of
`u32`. Also included is a saturating from/into trait allowing ergonomic
infallible conversion when you don't care if it saturates.

* Remove As from Balances trait

* Remove As from Aura module

* Remove As from Babe module

* Expunge `As` from contract

* Council module

* Democracy

* Finality tracker

* Grandpa

* First bit of indices

* indices

* Line lengths

* session

* system

* Staking

* Square up all other uses of As.

* RHD update

* Fix build/test

* Remove As trait

* line widths

* Remove final As ref

* Update srml/staking/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/client/src/cht.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/client/db/src/light.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* whitespace

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>
Co-Authored-By: André Silva <andre.beat@gmail.com>

* Bring back u32 check for number on CLI

substrate/core/cli/src/params.rs

@@ -533,11 +533,11 @@ pub struct ExportBlocksCmd {
 
 	/// Specify starting block number. 1 by default.
 	#[structopt(long = "from", value_name = "BLOCK")]
-	pub from: Option<u64>,
+	pub from: Option<u32>,
 
 	/// Specify last block number. Best block by default.
 	#[structopt(long = "to", value_name = "BLOCK")]
-	pub to: Option<u64>,
+	pub to: Option<u32>,
 
 	/// Use JSON output rather than binary.
 	#[structopt(long = "json")]
@@ -573,7 +573,7 @@ impl_get_log_filter!(ImportBlocksCmd);
 pub struct RevertCmd {
 	/// Number of blocks to revert.
 	#[structopt(default_value = "256")]
-	pub num: u64,
+	pub num: u32,
 
 	#[allow(missing_docs)]
 	#[structopt(flatten)]