replace imports of q with bluebird

```
find src spec -name '*.js' |
   xargs perl -i -pe 'if (/require\(.q.\)/) { $_ = "import Promise from '\''bluebird'\'';\n"; }'

find src spec -name '*.js' |
   xargs perl -i -pe 'if (/import q/) { $_ = "import Promise from '\''bluebird'\'';\n"; }'
```

src/http-api.js

@@ -18,7 +18,7 @@ limitations under the License.
  * This is an internal module. See {@link MatrixHttpApi} for the public class.
  * @module http-api
  */
-const q = require("q");
+import Promise from 'bluebird';
 const parseContentType = require('content-type').parse;
 
 const utils = require("./utils");