Ensure number format functions are consistent for i18n usage

[TheWitness]

Describe the bug

The current number_format() function in php considers a precision of NULL to be to show all the digits when applying the number_format() function. The Cacti wrapper number_format_i18n() does not perform identically. This leads to GUI's that often times do not look as you would expect them to.

To Reproduce

Steps to reproduce the behavior:

1. print a number > 10000 using number_format($somevalue);

2. print a number > 10000 using number_format_i18n($somevalue);

3. Note the differences

Expected behavior

Cactis number_format_i18n() should work identically to the number_format() standard php function.