Review file read/write operations

[bcoles]

BeEF reads and writes to various files within the BeEF application directory and user's home directory.

Ideally, BeEF should never write to the application directory.

BeEF writes to the user's home directory in only three instances:

# grep -rn "\$home_dir" core/ extensions/ modules/
core/logger.rb:15:      @logger ||= Logger.new("#{$home_dir}/beef.log").tap do |log|
modules/host/get_wireless_keys/module.rb:15:    filename = "#{$home_dir}/exported_wlan_profiles_#{ip}_-_#{timestamp}_#{@datastore['cid']}.xml"
modules/browser/spyder_eye/module.rb:28:      filename = "#{$home_dir}/screenshot_#{ip}_-_#{timestamp}_#{@datastore['cid']}.png"

Review whether some data, if any, should instead be stored in the database.

Investigate a consistent approach and standard practice guidelines for future development.