Make some T0 conditions handles optional

Motivated by https://its.cern.ch/jira/browse/ATR-21220

I'm trying to tidy up conditions data that has a read handle that is always required, even when the corresponding data does not exist. Here it seems that the configuration is conditional on isOnline, so I've cleared the handles otherwise, removing the dependency.

Please note that just not initialising a handle doesn't make it go away! You have to call initialize( false ). I changed one existing handle accordingly. Then I've removed a couple of the corresponding hacky fixes I had to make for view loading.

Would appreciate @sshaw taking a look to see if my logic is correct!