Configure filesystem paths from the command line

[hawkw]

Currently, all paths used by the server are hard-coded to paths in the directory where the server source code is located. On Unix systems, it's preferable to store state, configuration, and log files in different directories. Therefore, this commit adds the following new command-line arguments to configure these paths:

• --state-dir: configures the directory where the database and uploaded image files are stored.
• --config-path: configures the path to the config file.
• --log-path: configures the path to the directory where log files will be written.
• --lock-path: configures the path to the directory where the server will store its PID lock file.

If these command-line arguments are not provided, the server behaves identically to the way it does today.

Fixes #20

[SasaKaranovic]

This PR should be addressed by the #29