PLT-3633 EE: Add Google and Office365 SSO through OAuth2 (#3660)

* EE: Add Google and Office365 SSO through OAuth2

* Add localization strings

* Text tweaks for PLT-3633

* Added sign-up button for Office 365

* Updated some error messages and a bit of licensing

* Updated sign-in method section in user settings to include Google and Office365

* Added more localization strings

webapp/utils/constants.jsx

@@ -267,6 +267,7 @@ export const Constants = {
     OFFTOPIC_CHANNEL_UI_NAME: 'Off-Topic',
     GITLAB_SERVICE: 'gitlab',
     GOOGLE_SERVICE: 'google',
+    OFFICE365_SERVICE: 'office365',
     EMAIL_SERVICE: 'email',
     LDAP_SERVICE: 'ldap',
     SAML_SERVICE: 'saml',