add trailing slash on ROOT_URL for livechat installation script

needs a slash, else url will look like this:
`j.src = 'https://domain.tldpackages/rocketchat_livechat/assets/rocket-livechat.js';`

Fix pin and star

Fixed several english issues in the Incoming Webhooks settings page

Support Integration webhook calls originating from client browsers

Most modern browser will issue a pre-flight request with HTTP OPTION method before the actual asynchronous POST.    This adds a CORS supporting option endpoint.

[WIP] Livechat manager

Changes to layout and added infinite scroll to mentions bar

Mentions bar

Conflicts:
	server/methods/loadHistory.coffee

Adjust layout direction based on user's language

Debug level setting - closes #1687