Fix catching polymorphic type by value

Replace catching polymorphic type std::bad_alloc 'by value'
with 'by reference'.
Pointed by gcc8

Debugger: Refactor SettingsManager.

- SettingsManager is now a pure virtual interface. The debugger core provides
a no-op implementation of it which is used by default if no explicit manager
is provided by the client requesting a new TeamDebugger. This allows consumers
of the debugger core that have no need for settings persistence such as the
report generator to not have to care about that particular detail at all.
- Add subclass DebuggerSettingsManager which is essentially the previous
existing implementation. This one will go with the application portion
of the Debugger once the separation of app and lib has been completed.
Adjust callers accordingly.