Rewrite the tool_customlang renderers

To be tested only with Boost (because MDL-58427 will get rid of old, bootstrapbase, themes for 3.7). Tool customlang functionality: changed strings Login as admin Navigate to Site Administration -> Language -> Language customisation Select a language pack and open the language pack for editing Choose the moodle.php file and click show strings Change a language string Save the changes to the language pack Open the language pack for editing again Verfiy  you see the changed language string Verify  the background colour for the changed language string row has changed. Tool customlang functionality: modified strings Navigate to Site Administration -> Language -> Language customisation Open the English language pack for editing Choose the moodle.php file and click show strings Change string "abouttobeinstalled" to "Bla Bla" Save changes edit the file lang/en/moodle.php Search for $string ['abouttobeinstalled'] and change its value to "Test" Save changes and purge caches Navigate to Site Administration -> Language -> Language customisation Open the English language pack for editing Choose the moodle.php file and click show strings Verify  the string "abouttobeinstalled" shows your original translation "Bla Bla" Verify the string row for "abouttobeinstalled" has a warning color background. Tool customlang: mobile design Navigate to Site Administration -> Language -> Language customisation Open the English language pack for editing Choose the moodle.php file and click show strings Change your browser size to a tablet size or use a tablet Verify the design looks similar to: Change your browser size to a mobile size or use a mobile Verify the design looks similar to: