[ticket/11928] Replace AJAX loading popup with animation.

PHPBB3-11928
[ticket/11928] Make sure the indicator is on top of other elements.

PHPBB3-11928
[ticket/11928] Rename loadingAlert to loading_indicator.

PHPBB3-11928
[ticket/11928] Javascript requires camel case.

PHPBB3-11928
Merge remote-tracking branch 'prototech/ticket/11928' into develop

# By Cesar G
# Via Cesar G
* prototech/ticket/11928:
  [ticket/11928] Javascript requires camel case.
  [ticket/11928] Rename loadingAlert to loading_indicator.
  [ticket/11928] Make sure the indicator is on top of other elements.
  [ticket/11928] Replace AJAX loading popup with animation.