Contract change to support KillBounty interface

[stellarmagnet]

Currently, Projects.sol does not support the KillBounty function in StandardBounties.sol.

In order for us to kill bounties from the Projects app, we need to connect this function to our Projects.sol contract.
This requires adding KillBounty to the Projects Bounties interface.

In addition, we need an extremely simple function to clean up any local bounty state in Projects.sol and trigger the KillBounty function on the StandardBounties contract. This function should have a unique ROLE associated with it and should trigger an internal function. These functions should have the following signatures:

function removeBounties( bytes32[] _repoIds, uint256[] _issueNumbers) public auth(REMOVE_ISSUES_ROLE)
function _removeBounty( bytes32 _repoId, uint256 _issueNumber) internal

The kit will also need to be updated to set the REMOVE_ISSUES_ROLE, this role will need to be added to the arapp.json file, and the function will need to be tested in projects.test.js.