load graphs from mavgraphs.xml

def load_graphs():
    '''load graphs from mavgraphs.xml'''
    mestate.graphs = []
    gfiles = ['mavgraphs.xml']
    if 'HOME' in os.environ:
        for dirname, dirnames, filenames in os.walk(os.path.join(os.environ['HOME'], ".mavproxy")):
            for filename in filenames:
                if filename.lower().endswith('.xml'):
                    gfiles.append(os.path.join(dirname, filename))
    elif 'LOCALAPPDATA' in os.environ:
        for dirname, dirnames, filenames in os.walk(os.path.join(os.environ['LOCALAPPDATA'], "MAVProxy")):
            for filename in filenames:
                if filename.lower().endswith('.xml'):
                    gfiles.append(os.path.join(dirname, filename))

    for file in gfiles:
        if not os.path.exists(file):
            continue
        graphs = load_graph_xml(open(file).read(), file)
        if graphs:
            mestate.graphs.extend(graphs)
            mestate.console.writeln("Loaded %s" % file)
    # also load the built in graphs
    try:
        dlist = pkg_resources.resource_listdir("MAVProxy", "tools/graphs")
        for f in dlist:
            raw = pkg_resources.resource_stream("MAVProxy", "tools/graphs/%s" % f).read()
            graphs = load_graph_xml(raw, None)
            if graphs:
                mestate.graphs.extend(graphs)
                mestate.console.writeln("Loaded %s" % f)
    except Exception:
        #we're in a Windows exe, where pkg_resources doesn't work
        import pkgutil
        for f in ["ekf3Graphs.xml", "ekfGraphs.xml", "mavgraphs.xml", "mavgraphs2.xml"]:
            raw = pkgutil.get_data( 'MAVProxy', 'tools//graphs//' + f)
            graphs = load_graph_xml(raw, None)
            if graphs:
                mestate.graphs.extend(graphs)
                mestate.console.writeln("Loaded %s" % f)
    mestate.graphs = sorted(mestate.graphs, key=lambda g: g.name)