Add automatic config discovery
Add automatic config discovery

This patch introduces to Augur the ability to use a config file
that is located outside of the current directory. Before, Augur would
only work correctly if one ran the `augur run` command in the same
directory as the config file. Now, Augur will automatically check a few
different places for a config file before erroring out. In order of precedence,
Augur will check the following locations:

1. The current directory
2. The root augur/ directory (where the git information is stored)
3. /opt/augur/
4. The path specified by the AUGUR_CONFIG_FILE environment variable

Augur will use the first config it finds when searching through these locations,
and the corresponding path will be logged to the terminal.

Signed-off-by: Carter Landis <ffc486ac0b21a34cfd7d1170183ed86b0f1b04a2@pm.me>

OSSHealth/ghdata,OSSHealth/ghdata,OSSHealth/ghdata