Allow specifying databases cache folder

[GitSquared]

See:
GitSquared/edex-ui#937
#8

This has two major problems:

• If we allow specifying a cache folder, can we still pre-download databases as an installscript?
• We might consider that the cache folder may be deleted/empty, and so we need to handle that too

Implementation might need making breaking changes releasing a new major version

Alternative: maybe default to OS-level temp dir?

[GitSquared]

published in v2.0.0