Add additional files for environment configuration

Bash and screen files
Added generic functions to shell file

which_shell -> Figures out current_shell (generic between bash and ZSH)
rload       -> Load configuration file
Removed '.' at the begining of filenames
Renamed bashrc-> Shell_common/posix.sh
added header to file

which_shell -> Figures out current_shell (generic between bash and ZSH)
rload       -> Load configuration file