Add notice about deprecated Crowdsales (#2116)

* Remove crowdsales from sidebar documentation, add links to old version

* Remove mentions of Crowdsales from the documentation

contracts/payment/escrow/RefundEscrow.sol

@@ -10,8 +10,7 @@ import "./ConditionalEscrow.sol";
  * @dev The primary account (that is, the contract that instantiates this
  * contract) may deposit, close the deposit period, and allow for either
  * withdrawal by the beneficiary, or refunds to the depositors. All interactions
- * with `RefundEscrow` will be made through the primary contract. See the
- * `RefundableCrowdsale` contract for an example of `RefundEscrow`’s use.
+ * with `RefundEscrow` will be made through the primary contract.
  */
 contract RefundEscrow is ConditionalEscrow {
     enum State { Active, Refunding, Closed }

contracts/token/ERC20/ERC20Pausable.sol

@@ -7,9 +7,9 @@ import "../../lifecycle/Pausable.sol";
  * @title Pausable token
  * @dev ERC20 with pausable transfers and allowances.
  *
- * Useful if you want to stop trades until the end of a crowdsale, or have
- * an emergency switch for freezing all token transfers in the event of a large
- * bug.
+ * Useful for scenarios such as preventing trades until the end of an evaluation
+ * period, or having an emergency switch for freezing all token transfers in the
+ * event of a large bug.
  */
 contract ERC20Pausable is ERC20, Pausable {
     /**

docs/modules/ROOT/nav.adoc

@@ -5,7 +5,6 @@
 * xref:tokens.adoc[Tokens]
 ** xref:erc20.adoc[ERC20]
 *** xref:erc20-supply.adoc[Creating Supply]
-*** xref:crowdsales.adoc[Crowdsales]
 ** xref:erc721.adoc[ERC721]
 ** xref:erc777.adoc[ERC777]
 

docs/modules/ROOT/pages/gsn.adoc

@@ -6,7 +6,7 @@ If you're new to the GSN, you probably want to first take a look at the xref:lea
 
 == Receiving a Relayed Call
 
-The first step to writing a recipient is to inherit from our GSNRecipient contract. If you're also inheriting from other contracts, such as ERC20 or Crowdsale, this will work just fine: adding GSNRecipient to all of your token or crowdsale functions will make them GSN-callable.
+The first step to writing a recipient is to inherit from our GSNRecipient contract. If you're also inheriting from other contracts, such as ERC20, this will work just fine: adding GSNRecipient will make all of your token functions GSN-callable.
 
 ```solidity
 import "@openzeppelin/contracts/GSN/GSNRecipient.sol";

docs/modules/ROOT/pages/index.adoc

@@ -47,7 +47,7 @@ To keep your system secure, you should **always** use the installed code as-is,
 The guides in the sidebar will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
 
 * xref:access-control.adoc[Access Control]: decide who can perform each of the actions on your system.
-* xref:tokens.adoc[Tokens]: create tradeable assets or collectives, and distribute them via xref:crowdsales.adoc[Crowdsales].
+* xref:tokens.adoc[Tokens]: create tradeable assets or collectibles, like the well known xref:erc20.adoc[ERC20] and xref:erc721.adoc[ERC721] standards.
 * xref:gsn.adoc[Gas Station Network]: let your users interact with your contracts without having to pay for gas themselves.
 * xref:utilities.adoc[Utilities]: generic useful tools, including non-overflowing math, signature verification, and trustless paying systems.