Refactor Library

The launcher code was in a position ripe for sphagetti, so this rewrites it in a more robust way.
In addition to cleaner code, this provides the following changes:
- Removal of obsolete Mojang authentication
- The rebasing of some internal state into a Sled database
- Tweaks which make some internal mechanisms more robust (e.g. profiles which fail to load can be removed)
- Additional tooling integration such as direnv
- Distinct public API to avoid messing with too much internal code
- Unified error handling in the form of `theseus::Error` and `theseus::Result`

.gitignore

@@ -3,9 +3,10 @@ node_modules/
 .svelte-kit/
 theseus_gui/build/
 WixTools
+.direnv/
 
 [#]*[#]
 
 # TEMPORARY: ignore my test instance and metadata
-theseus_cli/launcher
 theseus_cli/foo
+