[Enhancement] [RHEL/6] Add RHEL-6 gconf rule's remediations

This proposal operates on the following four RHEL-6's gconf's rules:
* ```Set GNOME Login Inactivity Timeout```,
* ```GNOME Desktop Screensaver Mandatory Use```,
* ```Enable Screen Lock Activation After Idle Period```, and
* ```Implement Blank Screensaver```

and for each of them performs two things:
* replace existing XCCDF ID & profile references with the particular OVAL check ID for name consistency,
* add (RHEL-6 specific) remediation script

Testing report:
--
The change has been tested on RHEL-6 & works as expected (for each of the four new remediation scripts).

Note for testing of ```Set GNOME Login Inactivity Timeout```  rule - in case you will be verifying directly via bash, be sure to export ```inactivity_timeout_value``` variable first. E.g via something like:

``` export inactivity_timeout_value=15```

Otherwise the remediation script won't work properly. The remaining three rules / remediations should work properly with any special care (AFAICT).

Please review.

Thank you, Jan.