Revert "Remove add_setting calls in backtrace_cleaner"

This reverts commit ae7fb79b38365420a2cd9bb2e6ea9672b161191f.
Change the default inclusion behaviour of the backtrace cleaner

By default the current working directory will only be included if it
matches one of the exclusion patterns

Signed-off-by: Sam Phippen <samphippen@googlemail.com>
Add some documentation for new backtrace behaviuor, move old docs.

Signed-off-by: Sam Phippen <samphippen@googlemail.com>
Swap in new exclude/include language in backtrace_cleaner_spec

Signed-off-by: Sam Phippen <samphippen@googlemail.com>
Add specs for new default behaviour of backtrace cleaner.

Signed-off-by: Sam Phippen <samphippen@googlemail.com>