api: Updates to Makefile and configuration files.

- Re-organized and documented make targets.
- Parameterized the make targets to more cleanly support multiple
  development scenarios.
- Documented the different development scenarios in a README.
- Standardized the host port used when running locally.
- Updated DEV and PROD database config files to match current practice.
- Renamed `personal_measure_api.config.prod.json` to
  `personal_measure_api.config.docker.json` to more accurately reflect
  that this is the config used when building the docker image
  (regardless of which env it ends up in).

api/database-dev.json

@@ -1,5 +1,5 @@
 {
   "driver": "postgres",
-  "connectionString": "host=localhost port=5999 dbname=personal_measure_dev user=postgres",
+  "connectionString": "host=localhost port=5432 dbname=personal_measure_dev user=pmapi",
   "sqlDir": "src/main/sql/migrations"
 }