[Feature Request] Allow setting a different directory for the user preferences & chat logs

Summary

Alchemy (Beta) already allows setting the cache directory to a different place from the default, which is very useful if you're either placing the cache on a different drive, or coalescing all viewer caches in the same directory (as I do). Please do the same for the user preferences/chat log directory.

Why is this improvement important to you? How would it benefit the community?

Because in SL all items are uniquely identified by an UUID and are immutable, this leads to a very simple disk cache system. As such, it can be freely shared with other SL viewers (namely, preview/beta versions) to save disk space — instead of having several separate caches, one for each viewer, side by side, you can simply throw them all together in the same place. This is quite useful (with only the slight drawback that when one of the viewers clears the cache, all will have it cleared) and already supported by Alchemy (Beta). Even OpenSimulator caches can all share the same directory; after all, OpenSimulator UUIDs will never conflict with SL's (and vice-versa), no matter what grid you're on.

What is missing is giving a possibility to do the same with the directory where all user settings are stored, as well as the chat logs. These are also, generically speaking, common across all viewers — configurations are usually plain XML files, using a well-defined format which is consistent between all, while logs are just text files, all written in the same format as well.

The ability to do so (as used by other TPVs such as the Cool VL Viewer) allows a much smoother transition between viewers. For instance, when moving out of the SL official viewer to Alchemy (or from Second Life to OpenSimulator and back), it is most useful to keep around the same camera and display settings (especially if these have been changed/added to and are tweaked to specific usage — such as doing benchmarks, or for some photography/machinima). It's also beneficial that the back chat log is kept the same across different viewers — or else it becomes a nightmare to figure out which viewer we used to send that super-important IM to a close friend.

Note that, under Unix-like environments (macOS and Linux) you can simply add a symbolic link instead. But that's neither user-friendly, nor guaranteed to survive an Alchemy upgrade; it might get silently overwritten with the default (empty) configuration without notice. If, by contrast, Alchemy is aware of the real location of the configuration files, it might be able to avoid that step.

Screenshots, Mockups, etc