Feature: Add config keys to specify config, db and transcoding directory individually

Currently there is a single "config" folder where the server looks for config files. The server also hard codes the sqlite database path to the config directory. On a traditional (ie., non-docker) installation, a user might want to specify these individually. The transcoding temp directory is determined through an algorithm that involves reading the $HOME or $XDG_CACHE_HOME env vars and appending olaris/transcoding. This would also be nice to specify through a config key.

We could keep the current locations as defaults in order to not break existing installs. I propose adding two config keys:

OLARIS_TRANSCODING_CACHE_DIR OLARIS_SQLITE_DIR

that would override these default locations.