Move DB versioning to separate file.
Do not use escape tables when compressing, they are not useful.
Retain in decompresser for backwards compatibility.
Move user DM indexes to their own DB table, and their own map.
Clear/no longer create dmindex column in users DB table.
Control DM index dirtyness separately from user object.

This is in part preparation for future work on on-demand loading of user
objects.

Adjust error message for invalid decompression tags to include the tag value.
Remove struct dbseltweetmsg_netfallback and DBSTMF::NET_FALLBACK flag.

These are not useful given that, as used, fallback will never.
This is as the single user checks ad.unloaded_db_tweet_ids first anyway.