Upgrade basics and ports chapters

• Changes in basics chapter:
  • Improve the rendering of the tables
  • Improve titles, show text instead of showing a command
  • Upgrade information about the "removing user procedure"
  • Upgrade "Directory Structure" based on hier.7
  • Run all the commands and check that the correct output is displayed

• Changes in ports chapter:
  • Simplify the way the user search for packages
  • Some minor changes in software packages examples, use Nginx instead of Apache, etc.
  • Improve the pkg bootstrap and show the current way. Remove references of FreeBSD 9 and 10.
  • Add information about how to configure pkg
  • Update information on how to handle packages: search, install, update, remove, etc.
  • Put the information on how to handle packets in order
  • Add information on how to block and unblock packages

• Global:
  • Add alt text to all of the images
  • Improve the AsciiDoc

Reviewed by: karels@, bcr@, arrowd@, jrm@