lib: Add global config namespace
unit-tests: Add basic tests for settings_t
unit-tests: Add tests for setters in settings_t
unit-tests: Add tests for enumerators in settings_t
settings: Allow empty strings in section key
unit-tests: Add tests for includes and file loading in settings_t
settings: Make print_key() not rely on null-terminated beginning of key buffer

The key to print (e.g. until the next .) still has to be
null-terminated.
settings: Add method that allows to define fallback sections for other sections

The fallbacks are currently only used for single value lookups.
Enumerators are not affected by them.
unit-tests: Test how settings_t handles some invalid data
lib: Add default config fallback for configured namespace

All settings in the configured global namespace fall back to libstrongswan.
lib: All settings use configured namespace
attr-sql: Use namespace for attr-sql config, with fallback
libtls: Move settings to <ns>.tls with fallback to libtls
libhydra: Use lib->ns instead of hydra->daemon
libhydra: Remove unused hydra->daemon
libcharon: Use lib->ns instead of charon->name
charon-tkm: Use lib->ns instead of charon->name
libcharon: Remove unused charon->name
array: Add array_sort function
array: Add array_bsearch function