Merge pull request #1510 from RocketChat/block-registration

i18n/en.i18n.json

packages/rocketchat-lib/server/functions/setUsername.coffee

packages/rocketchat-lib/server/startup/settings.coffee

packages/rocketchat-ui-admin/admin/admin.html

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

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

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

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

server/lib/accounts.coffee

server/methods/getUsernameSuggestion.coffee

server/methods/registerUser.coffee