Move server API routes to /api/ path?

[pdehaan]

Ref: #506 (comment)

We should only render the notfound page for HTML endpoints; some of the 404s are API endpoints and will not be expecting a notfound HTML page.

Not sure if we should rename some API routes in server/server.js so all API routes are under some /api/ prefixed path so they are a bit more obvious.

Proposal:

CURRENT	PROPOSED
app.get('/exists/:id', ...)	app.get('/api/exists/:id', ...)
app.get('/assets/download/:id', ...)	app.get('/api/download/:id', ...)
app.post('/delete/:id', ...)	app.post('/api/delete/:id', ...)
app.post('/upload', ...)	app.post('/api/upload', ...)

But I don't think this would apply to the following routes:

• app.get('/')
• app.get('/unsupported/:reason')
• app.get('/legal')
• app.get('/jsconfig.js')
• app.get('/download/:id')
• app.get('/__lbheartbeat__')
• app.get('/__heartbeat__')
• app.get('/__version__')