Multiple "configuration" files

Right now, IPFS Desktop is storing its configuration in two different places:

1. Here, for both logs and config.json.
2. ~/.ipfs-desktop for other files such as IPFS_PATH.

@lidel shared his concern on #1079 about it:

Digression: I am worried this separate file will produce bugs in the long run. Additional code is required to keep it in sync with config.json and we need to remember about it. This concern should not block this PR form being merged, just something to think about :)

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We're using ~/.ipfs-desktop for things that must be easily accessible from other scripts: it's a well-known location and it works cross-platform!

The application is now small, and the burden of maintenance of this specific topic is not really bug, but might be something to think about in the future!