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
- some indentation fixes
- move macdockiconhandler.h include in bitcoin.cpp to the "our headers"
  section
Merge pull request #2588 from Diapolo/GetBoolArg

remove GetBoolArg() fDefault parameter defaulting to false