Utilize CDN to improve performance

[vleong2332]

As tD grows, we need to consider using CDN to help performance.

@klappy pointed out possible concurrency issue that could lead to accidental DDoS attack with td.unfoldingword.org/exports/langnames.json endpoint.

Right now, we increase the web service replica to 4 from 1. This will temporarily alleviate the issue and may have long-term billing implications, For long-term solution, we need to consider using CDN and/or router caching.