PLT-2258 Unified login screen and related APIs (#2820)

* Unified login screen and related APIs

* Refactored login API call to be less convoluted

* Removed LDAP login prompt from invite process

* Fixed existing LDAP users being able to log in if LDAP was configured, but disabled

* Gofmt

* Future proofed login API

* Updated login APIs based on feedback

* Added additional auditing to login API

* Actually removed loginById

api/channel_benchmark_test.go

@@ -131,7 +131,7 @@ func BenchmarkJoinChannel(b *testing.B) {
 	user = th.BasicClient.Must(th.BasicClient.CreateUser(user, "")).Data.(*model.User)
 	LinkUserToTeam(user, th.BasicTeam)
 	store.Must(Srv.Store.User().VerifyEmail(user.Id))
-	th.BasicClient.LoginByEmail(th.BasicTeam.Name, user.Email, "pwd")
+	th.BasicClient.Login(user.Email, "pwd")
 
 	// Benchmark Start
 	b.ResetTimer()