Also, set gargantext-settings.toml as the default file

Remove the calls to `recvMalloc` in favour of using the (patched) `recv`
from the original nanomsg library, which shouldn't segfault anymore. The
reason for using `recv` are a few, but mostly the fact that `recv` can
allocated arbitrary-long payloads data (up to the 1MB limit) without an
hardcoded limit like `recvMalloc` was imposing. Furthermore, `recv` does
resource cleanup for us via `c_nn_freemsg`, whereas `recvMalloc` is not
thread/exception safe. Consider the implementation:

```
recvMalloc :: Receiver a => Socket a -> Int -> IO ByteString
recvMalloc (Socket t sid) numBytes = do
  ptr <- mallocBytes numBytes
  -- receive by blocking the thread
  len <- c_nn_recv sid ptr (#const NN_MSG) 0 -- (#const NN_DONTWAIT)
  str <- C.packCStringLen (castPtr ptr, fromIntegral len)
  free ptr
  return str
```

If any exception (synchronous or asynchronous) strikes _before_ the call
to `free`, we would be leaking C memory.

The `Dispatcher` type is now opaque and not exported by
`.AsyncUpdates.Dispatcher`, and it has been moved out of the `.Types`.

This ensures that we can make the internal record fields private, and
offer accessors for things like `terminateDispatcher`. This preserve
information hiding and allows us to change the internal way of
terminating a dispatcher (for example switching away from normal
`forkIO` in favour of `async` & co) while not breaking client's code.

This commit refactors the common pattern `bracket init deinit use` in
`withNotifications` in `drivers.hspec.Main`, so that `withNotifications`
in atomic and the user doesn't incur in the pattern of using the init
and deinit functions independently from the `bracket`.

To be faithful about what I preach, we should do the same for
`startCoreNLPServer` and `stopCoreNLPServer`.

This commit tightens up the public API exposed by the Dispatcher,
for similar reasons as we had for the CentralExchange.

This commit tigthen the public API for the `.CentralExchange` module,
so that it's clear which are the exported (public) functions, and
we do not leak the transport layer used by the central exchange

Also, tests pass now, locally