dvb-c: default to SYS_DVBC_ANNEX_AC
Merge remote-tracking branch 'tornblom/dvb-rewrite' into feature/dvb-rewrite
idnode: added some rate limiting to idnode update messages
idnode: several improvements to the auto-updating features.

This can now be disabled via tick-box at bottom of the grid and no data
is actually sent in the update, just which nodes have been updated.

There is still an inefficiency in that a bunch of nodes being updated could
result in loads of reloads, but that could be improved with a bit of client
side buffering/delay.