This is in reference to #1161 - "Static files not properly reloaded by all browsers after update".

* Change the `BUILD_ID` context variable implementation into use of the `static` template tag.
* Refactored templates that were using the `BUILD_ID` context variable above.
* Re-use the `static` template tag of the `staticfiles` app into the new `distributed/templatetags/kalite_staticfiles.py`.  So we don't have to modify static files that were using the `static` tag.
* Some minor fixes to templates on incorrect html tags.
Add hash to `khan-lite.css`.
Use boolean values as second argument to custom `static` template tag, defaults to False.
Added option to use `fle_utils.config.models.Settings` that can be set at the admin site.
Options for hash now starts with the `Settings`, then the `BUILD_ID`, then the `SHA256` hash.
Merge pull request #2075 from cpauya/feature/1161-staticfiles-after-update

Feature/1161 staticfiles after update