migrate to java 8

ring-android/app/build.gradle

...in/java/cx/ring/about/AboutBottomSheetDialogFragment.java

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

...roid/app/src/main/java/cx/ring/account/AccountWizard.java

...id/app/src/main/java/cx/ring/account/AccountsAdapter.java

...rc/main/java/cx/ring/account/ConfirmRevocationDialog.java

...roid/app/src/main/java/cx/ring/account/DeviceAdapter.java

...app/src/main/java/cx/ring/account/RegisterNameDialog.java

...app/src/main/java/cx/ring/account/RenameDeviceDialog.java

...ain/java/cx/ring/account/RingAccountCreationFragment.java

...main/java/cx/ring/account/RingAccountSummaryFragment.java

...oid/app/src/main/java/cx/ring/adapters/NumberAdapter.java

...pp/src/main/java/cx/ring/application/RingApplication.java

...ndroid/app/src/main/java/cx/ring/client/CallActivity.java

...ndroid/app/src/main/java/cx/ring/client/HomeActivity.java

.../main/java/cx/ring/contactrequests/BlackListFragment.java

...ain/java/cx/ring/contactrequests/BlackListViewHolder.java

...ava/cx/ring/contactrequests/ContactRequestViewHolder.java

.../java/cx/ring/contactrequests/ContactRequestsAdapter.java

...java/cx/ring/contactrequests/ContactRequestsFragment.java