Add user configurable config file
We want to create a user configurable config file that replaces various settings used globally by either Sia-UI for siad.
As a starter issue, the goal is to create a custom config that allows users to set the path of the Sia directory. Some hosts prefer to store their blockchain on a different path than the default AppDir paths. While you can accomplish this by running a separate instance of siad
- it would be more seamless to do this via a json file.