* Create template for the language import page.
* Apply Bootstrap classes to form elements.
* Use core notifications for displaying error/success messages.
Before this change if a language pack was updated by the
\tool_langimport\task\update_langpacks_task scheduled task, changes
would not be available to users until an admin manually cleared the
strings cache.
This change causes the cache to purged when a language pack it update,
this will cause it to rebuild so users will start seeing updates
automatically.
Similar to upgrade_language_pack(), update_langpacks_task should
respect skiplangupgrade config. Also, this should be added to behat
whitelist, so it can be disabled during on-sync period, when lang
pack for master is not available.
Zig Tan