LMDB: increase max readers for all databases (journal, kasp, timers..)

This has 2 consequences:

1) increased size of lock.mdb file (8k -> 80k)
this seems fine since the number of databases is limited for Knot
and independent on number of zones

2) possibly longer linear search in lock table upon txn_begin
however, it depends rather on real number of readers
than on maximum readers limit