Reduce bundle size and Analytics

New:

• added matomo analytics (#86)
• added stellarx to exchanges list
• set HTML page titles (#102 )

Reduced bundle size:

• moved directory images (exchange and anchor logos) out of json into separate files (~89k)
• replaced json2csv dependency with bespoke conversion function (~160k)
• dynamic route imports with react-loadable

Fixed:

• payment table headers (#100) (@danielheyman)
• build with yarn (#15)

Upgraded:

• upgrade stellar-sdk to 0.11.0
• upgrade nodejs engine to 10.x.x (LTS)