Merge pull request #5407 from RocketChat/importers-check-file-type-using-signature

package.json

packages/rocketchat-assets/package.js

packages/rocketchat-file-upload/package.js

packages/rocketchat-importer-csv/main.js

packages/rocketchat-importer-csv/server.js

packages/rocketchat-importer-hipchat-enterprise/main.js

packages/rocketchat-importer-hipchat-enterprise/server.js

packages/rocketchat-importer-hipchat/main.coffee

packages/rocketchat-importer-hipchat/server.coffee

packages/rocketchat-importer-slack/main.coffee

packages/rocketchat-importer-slack/server.coffee

...ages/rocketchat-importer/.npm/package/npm-shrinkwrap.json

...ocketchat-importer/client/admin/adminImportPrepare.coffee

.../rocketchat-importer/client/admin/adminImportPrepare.html

packages/rocketchat-importer/lib/importTool.coffee

...es/rocketchat-importer/server/classes/ImporterBase.coffee

...s/rocketchat-importer/server/methods/restartImport.coffee

...s/rocketchat-importer/server/methods/setupImporter.coffee