push-notification: PUSH_NOTIFICATION_USER_CONTEXT is now required Satisfies static analyzers

Updated copyright notices to include the year 2018.

push-notification: Switch to main ioloop while calling drivers' deinit/cleanup callbacks Continues a44595f7b1afc7ccbd8653598753b32899d01c76 to other functions. For example the OX backend would call http_client_wait(), which would move the I/Os and timeouts to the current ioloop, which might not be main_ioloop always. When that ioloop gets destroyed, I/O and timeout leaks are logged and eventually the process crashes when calling http_client_deinit() in cleanup() (this would happen later for another mail_user).

push-notification: Switch to main ioloop while calling drivers' commit callbacks There aren't any guarantees what ioloop happens to be active at the time the commit is called. The active ioloop can also be destroyed early on, which can cause an I/O leak and crashes later on.

Updated copyright notices to include the year 2017.

global: Require comparisons to be strict boolean expressions * No implicit integer -> boolean or pointer -> boolean conversions * !expr can be used only if expr is boolean type These were checked with a patched clang. It found various actual bugs, which were fixed by the previous commits.

global: freshen copyright git ls-files | xargs perl -p -i -e 's/(\d+)-201[0-5]/$1-2016/g;s/ (201[0-5]) Dovecot/ $1-2016 Dovecot/'

push-notification: OCD fix for lining up function parameters

push-notification: Removed optimization to init drivers only once. Different users may have different drivers. And the previous metadata-caching change especially isn't working without this change.

push-notification: Free all events at plugin deinit.

push-notification: Improved struct naming of driver list data

push-notification: On-demand initialization of transaction data

push-notification: Fix distinguishing between IMAP APPEND and MTA deliveries

Added push-notification plugin