Use boost-asio to improve FAIL* server performance

This patch overhauls the FAIL* server code to leverage Boost asio to be able to
handle a large number of clients (>4000). In this implementation the server is
now single threaded. I've not encountered any problems with this for up to
about 10k clients. Boost ASIO can also be used multithreaded, but I assume the
FAIL* internal data structures (Synchronized*) will become a bottleneck first.

The code now additionally depends on Boost Coro and Boost Context, as well as
a C++ 14 compiler, although the only C++14 feature required is a lambda capture
with initializer, such as [ x = std::move(x) ]. gcc-4.9.2 does this.

The code could (and probably should) be cleaned up more. Comments are wordy,
code is unnecessary now (multiple server threads), code is not self-contained
(headers spread dependencies), many ifdef's (server performance measuring
should be runtime rather than a compile time option), and much more. But for
this patch I was going for a minimal changeset the get the functionality in,
to have an easier review. Alas, FAIL* has no Unit-test suite to run the changes
against.

To handle such a large number of clients more changes were necessary, for
example server status output is now performed every 1s, instead for every
request.

The class Minion was removed completely; the only thing it was doing was
encapsulate an int.

The server has now a runtime-configurable port, or it can select a free port on
its own if none is specified. This requires the CampaignManager to add a port
argument and instantiate the JobServer dynamically.

Change-Id: Iad9238972161f95f5802bd2251116f8aeee14884

src/core/CMakeLists.txt

@@ -1,5 +1,5 @@
 ### Add Boost and Threads
-find_package(Boost 1.42 COMPONENTS thread REQUIRED)
+find_package(Boost 1.42 COMPONENTS thread coroutine context REQUIRED)
 include_directories(${Boost_INCLUDE_DIRS})
 link_directories(${Boost_LIBRARY_DIRS})