Increase testing coverage (#1195)

* Added non-target bounty test

* Increased ERC721 testing coverage.

* Addressed review comments.

* fix linter error

* Fixed linter error

* Removed unnecessary bouncer require

* Improved Crowdsale tests.

* Added missing SuperUser test.

* Improved payment tests.

* Improved token tests.

* Fixed ERC721 test.

* Reviewed phrasing.

contracts/access/SignatureBouncer.sol

@@ -82,7 +82,6 @@ contract SignatureBouncer is Ownable, RBAC {
     public
     onlyOwner
   {
-    require(_bouncer != address(0));
     removeRole(_bouncer, ROLE_BOUNCER);
   }
 

contracts/token/ERC721/ERC721BasicToken.sol

@@ -131,7 +131,6 @@ contract ERC721BasicToken is SupportsInterfaceWithLookup, ERC721Basic {
     public
   {
     require(isApprovedOrOwner(msg.sender, _tokenId));
-    require(_from != address(0));
     require(_to != address(0));
 
     clearApproval(_from, _tokenId);