Show more clear login error for Sandstorm users

Fixes #1328

.sandstorm/launcher.sh

 #!/bin/bash
 set -euo pipefail
 
+export METEOR_SETTINGS='{"public": {"sandstorm": true}}'
 exec node /start.js -p 8000

.sandstorm/sandstorm-pkgdef.capnp

@@ -91,6 +91,7 @@ const myCommand :Spk.Manifest.Command = (
   argv = ["/sandstorm-http-bridge", "8000", "--", "/opt/app/.sandstorm/launcher.sh"],
   environ = [
     # Note that this defines the *entire* environment seen by your app.
-    (key = "PATH", value = "/usr/local/bin:/usr/bin:/bin")
+    (key = "PATH", value = "/usr/local/bin:/usr/bin:/bin"),
+    (key = "SANDSTORM", value = "1")
   ]
 );

packages/rocketchat-ui-login/login/form.coffee

@@ -29,6 +29,9 @@ Template.loginForm.helpers
 	showBackToLoginLink: ->
 		return 'hidden' unless Template.instance().state.get() in ['register', 'forgot-password', 'email-verification', 'wait-activation']
 
+	showSandstorm: ->
+		return Template.instance().state.get() is 'sandstorm'
+
 	btnLoginSave: ->
 		switch Template.instance().state.get()
 			when 'register'
@@ -114,7 +117,10 @@ Template.loginForm.events
 
 Template.loginForm.onCreated ->
 	instance = @
-	@state = new ReactiveVar('login')
+	if Meteor.settings.public.sandstorm
+		@state = new ReactiveVar('sandstorm')
+	else
+		@state = new ReactiveVar('login')
 	@validate = ->
 		formData = $("#login-card").serializeArray()
 		formObj = {}

packages/rocketchat-ui-login/login/form.html

 <template name="loginForm">
+	{{#if showSandstorm}}
+		<div class="alert alert-danger">
+			You must login to Sandstorm (on the top right) in order to access this chat.
+		</div>
+	{{else}}
 	<form id="login-card" method='/'>
 		{{#if waitActivation}}
 			<header>
@@ -47,4 +52,5 @@
 	<div class='login-terms'>
 		{{{loginTerms}}}
 	</div>
+	{{/if}}
 </template>