Separate error_level for initialise & execute?

[tdealtry]

Currently, there is a single error_level option inside ToolChain

• 0= do not exit
• 1= exit on unhandeled errors only
• 2= exit on unhandeled errors and handeled errors

I naively envisage the best way to set things up is

• Mode 2 for Initialisation. There's no point running Execute if its setup incorrectly
• Mode 0 for Execute. Try to recover & try to run forever

I don't see any other way to setup a ToolChain like this, other than adding extra variables like this. Before making a PR, just wanted to check

• if I'm missing anything that allows this to be done as ToolChain currently is
• whether you think this is a sensible solution

Basically in TriggerApp we are using error_level=2, but then get weird seg faults if Initialisation fails