Add initial support for getting ChannelMember info of all bridges (#678)

* Add initial support for getting ChannelMember info of all bridges.

Adds an EventGetChannelMembers event, which gets send every x time to
all bridges. Bridges should respond on this event with a Message
containing ChannelMembers in the EventGetChannelMembers key in the
Extra field.

handleEventGetChannelMembers will handle this Message and sets the
contained ChannelMembers to the Bridge struct.

* Add ChannelMembers support to the slack bridge

bridge/bridge.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/42wim/matterbridge/bridge/config"
 	"github.com/sirupsen/logrus"
+	"sync"
 )
 
 type Bridger interface {
@@ -16,14 +17,16 @@ type Bridger interface {
 
 type Bridge struct {
 	Bridger
-	Name     string
-	Account  string
-	Protocol string
-	Channels map[string]config.ChannelInfo
-	Joined   map[string]bool
-	Log      *logrus.Entry
-	Config   config.Config
-	General  *config.Protocol
+	Name           string
+	Account        string
+	Protocol       string
+	Channels       map[string]config.ChannelInfo
+	Joined         map[string]bool
+	ChannelMembers *config.ChannelMembers
+	Log            *logrus.Entry
+	Config         config.Config
+	General        *config.Protocol
+	*sync.RWMutex
 }
 
 type Config struct {
@@ -37,15 +40,17 @@ type Config struct {
 type Factory func(*Config) Bridger
 
 func New(bridge *config.Bridge) *Bridge {
-	b := new(Bridge)
-	b.Channels = make(map[string]config.ChannelInfo)
+	b := &Bridge{
+		Channels: make(map[string]config.ChannelInfo),
+		RWMutex:  new(sync.RWMutex),
+		Joined:   make(map[string]bool),
+	}
 	accInfo := strings.Split(bridge.Account, ".")
 	protocol := accInfo[0]
 	name := accInfo[1]
 	b.Name = name
 	b.Protocol = protocol
 	b.Account = bridge.Account
-	b.Joined = make(map[string]bool)
 	return b
 }
 
@@ -54,6 +59,13 @@ func (b *Bridge) JoinChannels() error {
 	return err
 }
 
+// SetChannelMembers sets the newMembers to the bridge ChannelMembers
+func (b *Bridge) SetChannelMembers(newMembers *config.ChannelMembers) {
+	b.Lock()
+	b.ChannelMembers = newMembers
+	b.Unlock()
+}
+
 func (b *Bridge) joinChannels(channels map[string]config.ChannelInfo, exists map[string]bool) error {
 	for ID, channel := range channels {
 		if !exists[ID] {