sqlite3 database / asynchronous access to it

[laforge]

Sometimes we want to access the database but it might be locked, or the data might require reading some data off disk.

Due to the single-threaded non-blocking architecture of bsc_hack, this may cause all kinds of problems.

Either we have to treat the database as a separate process to which we send messages, or we have to simply cache all the data in RAM and only update the on-disk cache whenever convenient and/or at program exit time.