Serialize only CTransaction data in gettransaction RPC hex

Don't include trailing implementation-specific wallet metadata.
Fixes 3a1c20b.
Increase default dbcache to 100 MiB

Conflicts:
	src/init.cpp
add constants for shared (GUI/core) -dbcache settings

- adds nDefaultDbCache, nMaxDbCache and nMinDbCache in txdb.h

Conflicts:
	src/init.cpp
Update