HiveSigner integration

Description

Login and perform operations with HiveSigner.

For more details, please refer to https://peakd.com/hive-139531/@good-karma/imagehoster-hivesigner-and-condenser-bounty#@roomservice/re-good-karma-qd5qsb

The Merge Request contains almost the same change as condenser!74 (merged), except some minor differences.

Relevant Issues

Fixes: condenser#43 (closed)

src/app/utils/HiveSigner.js

@@ -49,7 +49,7 @@ export const setHiveSignerAccessToken = (
 
 export const sendOperationsWithHiveSigner = (ops, params, cb) => {
     if (!params) params = {};
-    if (!params.callback) {
+    if (!params.callback && isBrowser()) {
         params.callback = window.location.href;
     }
     const uri = encodeOps(ops, params);