Add settings to configure default file location

[douglance]

Is your feature request related to a problem? Please describe.

I have a repo full of markdown files that I want to sync to a shared file server(iCloud, Dropbox, Google Drive, etc.) as well as Git.

Describe the solution you'd like

An additional extension setting to be able to select where to keep the files synced by Gistpad on my local machine.

Describe alternatives you've considered

I've tried a bunch of other ways to sync my notes to all of my devices, and this is the simplest option.

Additional context

It'd be nice to be able to set the location based on project/gist but I understand the complexity of that request with the current UI might be tricky.