Feature: db file locking

[appy-one]

(H)appy new year! 🍾🥂

This PR helps preventing database corruption #48 by disallowing multiple processes to access the same database file simultaneously, unless they are using IPC for inter-process communication. This means that forked processes with pm2 or NodeJS clustering, or servers using acebase-ipc-server can still all access the database simultaneously, but all other processes that try to open an already open db will be denied access.

For its implementation I have modified proper-lockfile instead of adding it as a dependency for the following reasons:

• The proper-lockfile project appears not to be maintained (last commit Jan 2021), has old open issues
• package has no types
• code uses callbacks instead of promises
• has dependencies AceBase does not need

I changed the following:

• ported to TypeScript
• refactored callbacks to async promises
• removed signal-exit dependency (not needed)
• removed retry dependency (using own simple implementation)
• removed graceful-fs dependency (using own pfs)
• removed unused code (probably more to be removed later)

requires acebase-core #29 to be merged, dependency updated

[appy-one]

I'm parking this PR because I implemented an automatically starting up IPC service/"daemon" in #213, which acts as an automatic (local) IPC master for each process requesting access to the same database. Locking the file will therefore not be necessary.