fix unwrapping of nested exceptions

and enable stacktrace in responses if logging is set to trace
allow arithmetic operators on timestamps
implemented ``sys.cluster.settings`` expression
added parser support for `set global column = value`
implemented parser support for `RESET GLOBAL some_setting`
implemented sys.jobs in-memory table including collector
use UUID as job table key
access in memory tables directly instead of using a key
remove tableIdent from routing and isInMemory from TableInfo