make roles initializers idempotent

contracts/access/roles/CapperRole.sol

@@ -13,7 +13,9 @@ contract CapperRole is Initializable {
   Roles.Role private cappers;
 
   function initialize() public initializer {
-    _addCapper(msg.sender);
+    if (!isCapper(msg.sender)) {
+      _addCapper(msg.sender);
+    }
   }
 
   modifier onlyCapper() {

contracts/access/roles/MinterRole.sol

@@ -13,7 +13,9 @@ contract MinterRole is Initializable {
   Roles.Role private minters;
 
   function initialize() public initializer {
-    _addMinter(msg.sender);
+    if (!isMinter(msg.sender)) {
+      _addMinter(msg.sender);
+    }
   }
 
   modifier onlyMinter() {

contracts/access/roles/PauserRole.sol

@@ -13,7 +13,9 @@ contract PauserRole is Initializable {
   Roles.Role private pausers;
 
   function initialize() public initializer {
-    _addPauser(msg.sender);
+    if (!isPauser(msg.sender)) {
+      _addPauser(msg.sender);
+    }
   }
 
   modifier onlyPauser() {

contracts/access/roles/SignerRole.sol

@@ -13,7 +13,9 @@ contract SignerRole is Initializable {
   Roles.Role private signers;
 
   function initialize() public initializer {
-    _addSigner(msg.sender);
+    if (!isSigner(msg.sender)) {
+      _addSigner(msg.sender);
+    }
   }
 
   modifier onlySigner() {