Add application metrics for RPC latency, etc.

[hopskipnfall]

Adds the following config properties:

# Enables server metrics to be monitored and logged.
metrics.enabled=false
# How often the metrics should be saved to a file in seconds.
metrics.loggingFrequencySeconds=15

# Core number of threads to be used. Default value 5.
server.coreThreadpoolSize=5

Application-level and JVM metrics will be logged to CSV files in the metrics/ directory generated at runtime.

Also adds @AssistedInject onto some classes.