Hide concrete5 version number in upgrade page

If the constant APP_VERSION_DISPLAY_IN_HEADER is set to false,
unregistered visitors can still determine the currently installed
version by visiting the page /index.php/tools/required/upgrade.
Let's hide the version number when APP_VERSION_DISPLAY_IN_HEADER is
set to false.
Allow users to search for localized group

Groups are listed by their localized names. So, let's enable users to
perform searches by localized names...
https://hackerone.com/reports/4939

and some indenting
https://hackerone.com/reports/5420
minor fix
https://hackerone.com/reports/5417 Part 1
https://hackerone.com/reports/5417 Part 2
https://hackerone.com/reports/4930

Also cleaned it up a bit...
minor fix v2
https://hackerone.com/reports/5392
fixed disappearing pane header icons in chrome on click
reverted change and moving to the less file
really fixed disappearing pane header icons in chrome on click
Remove duplicate body reset

This line is called twice in the reset function:
$this->body = '';
https://hackerone.com/reports/4940
Fix php error when no cID is passed
Declare template variable as an empty string
Fix resetting template variable in reset method
Inherit page speed settings
check for defined constants