Added commands folder for client. Moved the login(...) func to login.c

*Added commands direcotry in src/client/ for holding sources and
headers used to perform ftp commands by the client

*Moved the login(...) function code from client.c to commands/login.c

*Added commands.h headfile containing all command related function
declarations, and later probarly structs and macros

*Added the process_commands.c source containing the process_commands(...)
function. It takes the user input and executes proper ftp commands using
the implemented functions that are declared in commands.h

*Added the login.c and process_commands.c to the Makefile