HTTP caching proxy

[damb]

Features and Changes:

• [STL] Allow prefixing routed URLs (at the time being, statically, only)
• [FED] Redirect fdsnws-station-* requests to HTTP caching proxy
• Currently, HTTP caching proxy is powered by Apache2 and mod_cache_disk
• The configuration fully relies on DNS
• Provide container setup

References and closes: #75

[damb]

Optionally, the cache expiration time could be configurable. Currently, the header processor defines an expiration time of 1800s.

[damb]

References: #50