use up/down/loseFocusHdl prevents a change of object cache
value while writing
the max. cache value is now set to 2047 MB as this prevents an
overflow of the configuration value

Change-Id: Ib98f7181b10e2875b2037e425eced3f12ba4c0b6
Reviewed-on: https://gerrit.libreoffice.org/20766Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Oliver Specht <oliver.specht@cib.de>