Periodically polls changes in gear configs.

Gear configs are persisted in a shared data storage (e.g. NFS) and are cached in ETS in each erlang node. Note that gear configs are loaded (cached into ETS) at each step of

• AntikytheraCore.start/2: all existing gear configs are loaded
• each gear's start/2: the gear's gear config is loaded

Thus this GenServer's responsibility is just to keep up with changes in the shared data storage.

Depends on AntikytheraCore.GearManager (when applying changes in gear configs results in update of cowboy routing).