MT#9177 Add yealink, change architecture and fix credentials store issue

Squashed commit of the following:

commit 79484a6e87392a7a335c590fc593cd2de321ba4f
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Wed Dec 3 02:11:23 2014 +0200

    MT#9177 We don't need update device_id in credentials.

    Rather usual thing.

commit d2161a9b3fe02f5617bec8ec61d31fe4caa31261
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Tue Nov 25 13:16:02 2014 +0200

    MT#9177 Return unregister into utils area.

commit ac8115bcc2641ef1a54be8319b65ff026f03e0a7
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Sun Nov 16 13:58:35 2014 +0200

    MT#9177 Yealink works

commit 51336e2b18d318d5acaa3d0fd1ab266ab7a25f5f
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Sun Nov 16 12:23:19 2014 +0200

    MT#9177 Yealink add_server

commit 6dc0fde8ddeee12b2ccddd5f2a1fe3c61387d9bc
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Fri Nov 14 09:54:14 2014 +0200

    MT#9177 Yealink url via serverName

commit ec00e658780b9a29c50bbe48def95852d1c30938
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Thu Nov 13 10:55:07 2014 +0200

    MT#9177 Yealink requires server length < 20

commit 0c29750e74983b3a1dcc89238a862ef31ae72d07
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Thu Nov 13 10:45:27 2014 +0200

    MT#9177 Wonderfully authorization for Panasonic started to work

    Without = at the end

commit 7d3c540a82524cb9ae31b64985f2ae08f3a7dd2a
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Thu Nov 13 10:36:51 2014 +0200

    MT#9177 Fix yealink authorization too

commit e39da24bc9ca3ba590695cafdacf7fe1ab925b7a
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Thu Nov 13 10:15:26 2014 +0200

    MT#9177 Small fixes for yealink

commit 9b9e2973eeca983672a6ca46fe5133a71fe928bb
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Thu Nov 13 08:12:33 2014 +0200

    MT#9177 Add yealink credentials fields

commit d63e9ab9672f6a38a8dbae146356e6b0ad2f8dd7
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Thu Nov 13 06:24:46 2014 +0200

    MT#9177 Some fixes for this layout

commit bd2a026ed4bdaed33a018e6bd866a9f94fbc0f35
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Wed Nov 12 22:43:37 2014 +0200

    MT#9177 Use custom bootstrap uri in this layout

commit bfd2f7a96c78486e714992f190281591f586f661
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Wed Nov 12 17:07:50 2014 +0200

    MT#9177 Further yealink changes

commit 3779466cb6c85228a48c445e2d619d8bb75d965f
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Wed Nov 12 15:55:47 2014 +0200

    MT#9177 Yealink added

commit 3fa77dcdb020cfdb11e9020b8365e8554354ac77
Author: Irina Peshinskaya <ipeshinskaya@sipwise.com>
Date:   Wed Nov 5 08:23:56 2014 +0200

    MT#9177 Refactor code to separate vendor specific and common logic

Change-Id: I41a912a5c8f90b3c58cf49b87a38a3b6a7b64bd6