Rename Applications -> Process, sort topologies by rank.

[tomwilkie]

Fixes #852

[paulbellamy]

$ ag -i application | grep -v vendor
...
experimental/_integration/easy_test.go:29:func TestApplications(t *testing.T) {
experimental/_integration/easy_test.go:31:      topo := parseTopology(t, httpGet(t, fmt.Sprintf("http://localhost:%d/api/topology/applications", appPort)))
experimental/_integration/easy_test.go:34:      have := parseEdge(t, httpGet(t, fmt.Sprintf("http://localhost:%d/api/topology/applications/%s/%s", appPort, "proc:node-192.168.1.1:wget", "theinternet")))
experimental/_integration/easy_test.go:59:      topo := parseTopology(t, httpGet(t, fmt.Sprintf("http://localhost:%d/api/topology/applications", appPort)))
experimental/graphviz/render.go:12:     "applications":         render.FilterUnconnected(render.ProcessWithContainerNameRenderer),
experimental/graphviz/render.go:13:     "applications-by-name": render.FilterUnconnected(render.ProcessNameRenderer),
...
render/detailed/node.go:98:     {report.Process, NodeSummaryGroup{TopologyID: "applications", Label: "Applications", Columns: []string{process.PID, process.CPUUsage, process.MemoryUsage}}},
render/detailed/node_test.go:104:               Label:      "Applications",
render/detailed/node_test.go:105:               TopologyID: "applications",
render/detailed/node_test.go:159:               Label:      "Applications",
render/detailed/node_test.go:160:               TopologyID: "applications",
...

[tomwilkie]

@paulbellamy PTAL