remove GetBoolArg() fDefault parameter defaulting to false

- explicitly set the default of all GetBoolArg() calls
- rework getarg_test.cpp and util_tests.cpp to cover this change
- use fTestNet instead of GetBoolArg("-testnet", false), if possible
  (hint: needed to take care of init order)
- some indentation fixes
- move macdockiconhandler.h include in bitcoin.cpp to the "our headers"
  section