Add get/set commands for settings

[mthalman]

Adds a settings get and settings set command to allow callers to retrieve and set the values of settings.

Because the settings in the settings file are hierarchical and represented as JSON, setting names use a dot-notation to separate the names to access the desired setting. For example: dredge settings get fileCompareTool.exePath gets the executable path of the file compare tool from the settings file.

Usage:

dredge settings get <name>

dredge settings set <name> <value>