gitignore cleanup

* ignore typical backup files created by common editors
* move general ignore rules like "*.o" or "depend.mk" to top level gitignore
* ignore executables and test directories in target dir gitignore
  as these are local and there's no general catch-all pattern for them
comment header
Merge branch 'hartmut-gitignore' of https://github.com/hholzgra/MaxScale into hholzgra-hartmut-gitignore
Merge branch 'hholzgra-hartmut-gitignore' into release-1.0beta-refresh
Add vi swap files