Merge branch 'acmedirectory_rebase' into 'master'

Use of ACME Directory and automatic update agreement to terms of service

* Update main script to:
  * Use the ACME directory to retrieve correct URLs from the ACME servers
  * Be able to update account informations (contact information and agreed terms of service)
  * Read terms of service links from either the ACME directory or account informations
  * Automatically update terms of service agreement with latest changes (user have to stay informed about the updates himself)
  * Fix HTTP errors handling
* Update configuration to:
  *  Configure ACME directory instead of CAUrl
  *  Allow to specify contact informations (email and phone number ; beware that Let's Encrypt servers don't allow phones)
* Update tests to:
  * Correctly setup before running tests without using global variable
  * Correctly clean setup after running tests (correctly remove ACME account and close temporary files)
  * Update requirements to latest dnspython release (as release 1.15 has fixed the dns updates issue)
* Update account delete script (you can find it in /tests/) according to updates of the main script

See merge request !5
1 job for 4-use-nonce-received-on-each-acme-response in 1 minute and 36 seconds (queued for 16 seconds)