Allow users to change default method of removing data sources when deleting graphs

[sysres-dev]

Is your feature request related to a problem? Please describe.
Our cacti users complained about some behaviour changes in the interface, we used cacti 0.8.8 for a long time, and they would like some behaviors closer to it :

• by default, when deleting graphs, the radio button is set to delete data sources as well, mistakes were made where user clicked 'continue' a bit too fast.

Describe the solution you'd like
It would be very nice to have new settings in global setting panel to choose cacti's behavior regarding this.

Describe alternatives you've considered
For now we solved thoses problems by hardcoding values in right places in the code :

Data source radio button change :

+++ cacti/graphs.php	
848c848
<                               form_radio_button('delete_type', '2', '2', __('Delete all Data Source(s) referenced by these Graph(s) that are not in use elsewhere.'), '1');
---
>                               form_radio_button('delete_type', '1', '2', __('Delete all Data Source(s) referenced by these Graph(s) that are not in use elsewhere.'), '1');
850c850
<                               form_radio_button('delete_type', '2', '1', __('Leave the Data Source(s) untouched.'), '1');
---
>                               form_radio_button('delete_type', '1', '1', __('Leave the Data Source(s) untouched.'), '1');

Additional context
Here are some stats about my Cacti installation:

Cacti Version | 1.1.38
Cacti OS | unix
RSA Fingerprint | 22:9a:ef:ad:d8:de:1d:e7:95:7d:89:98:bd:4f:b9:df
NET-SNMP Version | NET-SNMP version: 5.7.2
RRDtool Version | RRDtool 1.4.x
Devices | 26897
Graphs | 458451
Data Sources:
Script/Command: 16597
SNMP Get: 76962
SNMP Query: 291955
Script Query: 62267
Script Server: 26697
Script Query - Script Server: 31729
Total: 506207

[netniV]

Again, as per the graph lock option, this should be determined by a system setting not a user setting. Refer to the other two posts for hints on how to properly achieve it. Feel free to reach out to me by email if you want to consult on any of it.

[sysres-dev]

Implemented and merged in PR #2552, i'm closing the issue.