Fix #691 - System name not updating in system settings

[Fiveofoura]

Description

Page inputs in 'system settings', including 'system name', are sent via post request but do not get saved as only $_GET variables are included. A variable merging $_POST and $_GET replaces $_GET when looking for values after saving the system settings. Please see the following issue:

#691

Motivation and Context

As both $_GET and $_POST variables need to be read here from different parts of the system, combining both arrays into a new variable will fix the issue.

How To Test This

'admin' -> 'system settings'

Change the system name and save

System name should be changed when going back into system settings

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Final checklist

• My code follows the code style of this project found here.
• My change requires a change to the documentation.
• I have read the How to Contribute guidelines.