add basic import mechanisms

add fake import and import env, security, settings files
fix bug in settings precedence in _globals dict

variables could not be overwritten by later reference in another file
add a list of wrapped settings modules

accessible through _wrapped_modules list
add special flexi settings files to tests
add settings import to tests __init__
test for local settings import
test for FLEXI_RUN_ENV
fix a bug when settings name starts with '_'
more methods descriptions
get rid of the old code and mechanisms