multi-device: add device management pane

...id/app/src/main/java/cx/ring/client/AccountCallbacks.java

.../src/main/java/cx/ring/client/AccountEditionActivity.java

.../main/java/cx/ring/fragments/AdvancedAccountFragment.java

...rc/main/java/cx/ring/fragments/DeviceAccountFragment.java

...c/main/java/cx/ring/fragments/GeneralAccountFragment.java

.../main/java/cx/ring/fragments/MediaPreferenceFragment.java

.../main/java/cx/ring/fragments/SecurityAccountFragment.java

...oid/app/src/main/java/cx/ring/loaders/AccountsLoader.java

...in/java/cx/ring/service/ConfigurationManagerCallback.java

...droid/app/src/main/java/cx/ring/views/MenuHeaderView.java

.../main/res/drawable-hdpi/ic_desktop_windows_black_24dp.png

.../main/res/drawable-mdpi/ic_desktop_windows_black_24dp.png

...main/res/drawable-xhdpi/ic_desktop_windows_black_24dp.png

...ain/res/drawable-xxhdpi/ic_desktop_windows_black_24dp.png

...in/res/drawable-xxxhdpi/ic_desktop_windows_black_24dp.png

ring-android/app/src/main/res/layout/dialog_new_device.xml

ring-android/app/src/main/res/layout/frag_device_list.xml

ring-android/app/src/main/res/layout/item_device.xml

ring-android/app/src/main/res/values/strings_account.xml