If we're sending a html file to mobile-safari, do so as plain text.

This prevents safari from trying to render the page,
which it does because it ignores the "Content-Disposition" header.

services/web/app/coffee/Features/FileStore/FileStoreController.coffee

@@ -1,13 +1,22 @@
 logger = require('logger-sharelatex')
 FileStoreHandler = require("./FileStoreHandler")
 ProjectLocator = require("../Project/ProjectLocator")
- 
+_ = require('underscore')
+
+is_mobile_safari = (user_agent) ->
+	user_agent and (user_agent.indexOf('iPhone') >= 0 or
+									user_agent.indexOf('iPad') >= 0)
+
+is_html = (file) ->
+	file.name.lastIndexOf('.html') == file.name.length - 5
+
 module.exports =
 
 	getFile : (req, res)->
 		project_id = req.params.Project_id
 		file_id = req.params.File_id
 		queryString = req.query
+		user_agent = req.get('User-Agent')
 		logger.log project_id: project_id, file_id: file_id, queryString:queryString, "file download"
 		ProjectLocator.findElement {project_id: project_id, element_id: file_id, type: "file"}, (err, file)->
 			if err?
@@ -17,5 +26,9 @@ module.exports =
 				if err?
 					logger.err err:err, project_id: project_id, file_id: file_id, queryString:queryString, "error getting file stream for downloading file"
 					return res.sendStatus 500
+				# mobile safari will try to render html files, prevent this
+				if (is_mobile_safari(user_agent) and is_html(file))
+					logger.log filename: file.name, user_agent: user_agent, "sending html file to mobile-safari as plain text"
+					res.setHeader('Content-Type', 'text/plain')
 				res.setHeader("Content-Disposition", "attachment; filename=#{file.name}")
-				stream.pipe res
+				stream.pipe res