Switch bottle to using an 'app' instance.

This fixes the problem I was having (on two separate machines, Debian
stretch and Debian buster) with the Gateway not actually sending
messages out port 8500 to the Relay and Monitor.
  Something about the '@thing' syntax, or using bare 'run()' must be
interfering with zmq.green.  The latter ends up thinking there are no
active/matching sockets to send to[0], despite the sockets definitely
being there (complete with TCP 3-way handshake visible on tcpdump
output).
  With the problem:

	* no network traffic was observed on port 8500.
	* A test sender.send(...) just before the bottle run() call
	  *did* send the message.  A similar test at the start of the
	  @post('/upload/') function did not succeed.

[0] - I ended up putting debug prints in both python-zmq and the zeromq
'libzmq' libraries, building the Debian packages and installing those
versions.  I also ended up using 'gdb' on the process.  The end result
of this was to find that the _matching variable (a count of matching
sockets I think) was empty deep in libzmq, when it should be counting
sockets to send to.
  This was specifically in zeromq3-4.3.1/src/dist.cpp, in the
void zmq::dist_t::distribute (msg_t *msg_) function.  The immediate:

	    if (_matching == 0) {

test was true.  I didn't manage to track down which bit of libzmq code
should have been setting _matching before I 'recursed back up' the call
chain to investigate other things.

src/eddn/Gateway.py

@@ -21,7 +21,8 @@ from eddn.core.Validator import Validator, ValidationSeverity
 
 from gevent import monkey
 monkey.patch_all()
-from bottle import run, request, response, get, post
+from bottle import Bottle, run, request, response, get, post
+app = Bottle()
 
 logger = logging.getLogger(__name__)
 
@@ -158,7 +159,7 @@ def parse_and_error_handle(data):
         return "FAIL: " + str(validationResults.messages)
 
 
-@post('/upload/')
+@app.post('/upload/')
 def upload():
     response.set_header("Access-Control-Allow-Origin", "*")
     try:
@@ -181,7 +182,7 @@ def upload():
     return parse_and_error_handle(message_body)
 
 
-@get('/health_check/')
+@app.get('/health_check/')
 def health_check():
     """
     This should only be used by the gateway monitoring script. It is used
@@ -191,7 +192,7 @@ def health_check():
     return Settings.EDDN_VERSION
 
 
-@get('/stats/')
+@app.get('/stats/')
 def stats():
     response.set_header("Access-Control-Allow-Origin", "*")
     stats = statsCollector.getSummary()
@@ -211,7 +212,7 @@ class MalformedUploadError(Exception):
 def main():
     loadConfig()
     configure()
-    run(
+    app.run(
         host=Settings.GATEWAY_HTTP_BIND_ADDRESS, 
         port=Settings.GATEWAY_HTTP_PORT, 
         server='gevent',