o Synchronise the calls as there should be no drawback running
  in the background for a table flush.
o Locallise the after-filter hook to the two functions using it.
o Restrict the functionality to flush tables only.
o Remove some dead code along the way.

translation and coding style status_interfaces.php

PR: https://github.com/freebsd/pkg/issues/1424

This adds the following directories to avoid problems with
smaller embedded systems that do not have enough RAM:

	/var/cache/opnsense-update
	/var/cache/pkg

This is particularly bad for Nano systems with enough RAM
as it may grind the flash storage, but since this is a
"luxury" problem with Nano the scope is limited to that.
It's either being able to upgrade the firmware for all or
not at all.

FWIW, firmware upgrades will have to move to persistent
storage as soon as we hit FreeBSD 11 for the simple fact
that we'll have to do partial upgrade stages for the ABI
jumps of the kernel / base system anyway and cannot expect
to fetch more packages after reboot.

Proper garbage collection exists in both tools that shall
avoid overloading the persistant storage.

translation and style fixes

(hasync) add dns resolver to sync, service restart not included, probably needs a seperate page at some point. closes https://github.com/opnsense/core/issues/923

o restructure session open/close for better visibility
o remove potentially insecure "try again" button
o remove override for switching csrf off (defer)