Add remote syncing as import option

[Noevain]

Follow up from discord here

Opening this issue to confirm this change is wanted and discussion, I've been working on implementing the same subscription system MacroMate has but for WaymarkPreset, you can check progress on my fork

Essentially this would let users paste an URL and then keep their local library in sync with the remote one, checking for updates and only updating when asked by the user, only waymarks imported from URL would be affected.