reaction's configuration now has a state_directory optional member,
which is where it will save its databases. defaults to cwd.

added a lot of code necessary to properly test databases.
The new tests are currently failing, which is good : they'll permit
to hunt down this database consistency bug.

also removed some indirect dependencies via features removal,
and moved test dependencies to dedicated [dev-dependencies]

also small fix on an nft46.c function type and empty conf file
for ccls LSP server.