Database cache memory increased

As a result of growth of the UTXO set, performance with the prior default

database cache of 100 MiB has suffered.

For this reason the default was changed to 300 MiB in this release.

For nodes on low-memory systems, the database cache can be changed back to

100 MiB (or to another value) by either:

- Adding `dbcache=100` in bitcoin.conf

- Changing it in the GUI under `Options → Size of database cache`

Note that the database cache setting has the most performance impact

during initial sync of a node, and when catching up after downtime.