Error handling

[peterschrammel]

• replace asserts
• define basic exceptions (util/error.h / RFC: handling of fatal errors #1280)
• replace throws
• replace integer return codes where appropriate
• replace boolean return codes where appropriate
• clean up catches (lift to top-level and report to user in a single place)

[TGWDB]

Closing as this appears to be an idea/architecture request that is beyond the scope of a ticket here. Observations are that some of this is done/being done anyway. Please reopen if you believe this is erroneous.

[martin-cs]

Quite a lot of this was implemented with the introduction of the INVARIANTS and various clean-ups associated with it. There is still work to be done on this area though. I guess it depends how you feel about issues that are "This would be good to do at some point".