Few code improvements

Few code changes that I think could make users happy:

• submitting form is now done only by button value, I added submitting by button name and if button is replaced with image by image name
• logging in an user was now hard coded to 'Log in' this is now default but users can override it
• deleting user was done by hand, I changed it to use user_delete so if there are any custom hooks in place they will get called as well