Plugin split

[alexstaeding]

This PR tracks the work of splitting Catalyst into some distinct use-cases (one could even argue that these are separate plugins).

The idea is to extract as much logic as possible into common use-case agnostic modules and introduce use-case specific modules under the app/ directory. So far, these are:

Catalyst Droplet

• The use-case for single backend servers. Easiest installation, but lacks multi-server support.

Catalyst Breeze

• The only use-case previously covered by Catalyst, meant for single proxy deployments with multiple backend servers.
• Includes binaries for the proxy and backend servers.
• Other than the database, no external services required due to the use of plugin messaging.
• Easy installation

Catalyst Cyclone

• Built for scale, this is meant for large server deployments and supports redundancy and high availability. Supports multiple proxies.
• Includes binaries for the proxy and backend servers.
• Requires external services (such as a distributed key-value store) to support all features.
• Could potentially make use of the transfer packet and avoid the proxy completely.
• Much more complex installation compared to Breeze.