feat: add option to render json instead of hbs (#22)

Description
---
Add option to get json response instead of hbs. By calling any url with
`?json` parameter

Motivation and Context
---
It will be used in the react frontend.

How Has This Been Tested?
---
Manually.

What process can a PR reviewer use to test or verify this change?
---
Run the tari-explorer and change any url by adding `?json`.

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Breaking Changes
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- [x] None
- [ ] Requires data directory on base node to be deleted
- [ ] Requires hard fork
- [ ] Other - Please specify

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app.js

@@ -7,6 +7,7 @@ const path = require("path");
 const cookieParser = require("cookie-parser");
 const logger = require("morgan");
 const asciichart = require("asciichart");
+const cors = require("cors");
 
 var indexRouter = require("./routes/index");
 var blocksRouter = require("./routes/blocks");
@@ -87,6 +88,7 @@ app.use(
 );
 app.use(cookieParser());
 app.use(express.static(path.join(__dirname, "public")));
+app.use(cors());
 
 app.use("/", indexRouter);
 app.use("/blocks", blocksRouter);