Support rewriting messages from relaybots using ExtractNicks. Fixes #466 (#730)

some examples:
this replaces a message like "Relaybot: <relayeduser> something interesting" to "relayeduser: something interesting"
ExtractNicks=[ [ "Relaybot", "<(.*?)>\\s+" ] ]
you can use multiple entries for multiplebots
this also replaces a message like "otherbot: (relayeduser) something else" to "relayeduser: something else"
ExtractNicks=[ [ "Relaybot", "<(.*?)>\\s+" ],[ "otherbot","\\((.*?)\\)\\s+" ]
OPTIONAL (default empty)
ExtractNicks=[ ["otherbot","<(.*?)>\\s+" ] ]

gateway/handlers_test.go

@@ -0,0 +1,75 @@
+package gateway
+
+import (
+	"github.com/42wim/matterbridge/bridge"
+	"github.com/42wim/matterbridge/bridge/config"
+	"github.com/stretchr/testify/assert"
+
+	"testing"
+)
+
+func TestIgnoreEvent(t *testing.T) {
+	eventTests := map[string]struct {
+		input  string
+		dest   *bridge.Bridge
+		output bool
+	}{
+		"avatar mattermost": {
+			input:  config.EventAvatarDownload,
+			dest:   &bridge.Bridge{Protocol: "mattermost"},
+			output: false,
+		},
+		"avatar slack": {
+			input:  config.EventAvatarDownload,
+			dest:   &bridge.Bridge{Protocol: "slack"},
+			output: true,
+		},
+		"avatar telegram": {
+			input:  config.EventAvatarDownload,
+			dest:   &bridge.Bridge{Protocol: "telegram"},
+			output: false,
+		},
+	}
+	gw := &Gateway{}
+	for testname, testcase := range eventTests {
+		output := gw.ignoreEvent(testcase.input, testcase.dest)
+		assert.Equalf(t, testcase.output, output, "case '%s' failed", testname)
+	}
+
+}
+
+func TestExtractNick(t *testing.T) {
+	eventTests := map[string]struct {
+		search         string
+		extract        string
+		username       string
+		text           string
+		resultUsername string
+		resultText     string
+	}{
+		"test1": {
+			search:         "fromgitter",
+			extract:        "<(.*?)>\\s+",
+			username:       "fromgitter",
+			text:           "<userx> blahblah",
+			resultUsername: "userx",
+			resultText:     "blahblah",
+		},
+		"test2": {
+			search: "<.*?bot>",
+			//extract:        `\((.*?)\)\s+`,
+			extract:        "\\((.*?)\\)\\s+",
+			username:       "<matterbot>",
+			text:           "(userx) blahblah (abc) test",
+			resultUsername: "userx",
+			resultText:     "blahblah (abc) test",
+		},
+	}
+	//	gw := &Gateway{}
+	for testname, testcase := range eventTests {
+		resultUsername, resultText, _ := extractNick(testcase.search, testcase.extract, testcase.username, testcase.text)
+		assert.Equalf(t, testcase.resultUsername, resultUsername, "case '%s' failed", testname)
+		assert.Equalf(t, testcase.resultText, resultText, "case '%s' failed", testname)
+	}
+
+}