Fix issues with the updater

* Bad URLs used for downloading update files
* MD5ETagDownload resetting the expected ETag after failure to the failed file MD5 checksum
* Delete MD5ETagDownload downloaded files if the download fails.
Remove OSX hack that never worked anyway
Keep the last five logs
Initial FTB support. Allows "tracking" of FTB instances.
Make FTB instances behave better

* Do not re-create on every reload
* Use the version.json/custom.json logic properly
* Should be offline-friendly
* FTB instances can be copied, turn into normal instances
Fail if we fail to find the right forge version
FTB fixage

* Corrected an uninitialized variable that prevented forge list loadinf on Windows
* Run the update step twice for FTB instances to ensure forge libs get downloaded