Enabling img_sigs and add a toggle on the main screen

Have currently introduced most of the popular Linux images
and utilities for signature checking, if things go smoothly,
I'll continue to add addtional checks for the other images.

I'm currently avoiding development and rolling releases as the
files are typically not versioned and can introduce a lot of breakage
as the files can be replaced by build procedures and are difficult to
track.

If there are any problems, please open up an issue.

src/boot.cfg

@@ -16,7 +16,7 @@ set memdisk https://${boot_domain}/memdisk
 set sigs_enabled true
 
 # image signatures check enabled?
-set img_sigs_enabled false
+set img_sigs_enabled true
 
 # set location of signatures for sources
 set sigs http://${boot_domain}/sigs/

src/menu.ipxe

@@ -51,7 +51,8 @@ item --gap Tools:
 item utils ${space} Utilities
 item shell ${space} iPXE shell
 item netinfo ${space} Network card info
-item sig_check ${space} Signature Checks [ enabled: ${sigs_enabled} ]
+item sig_check ${space} netboot.xyz Signature Checks [ enabled: ${sigs_enabled} ]
+item img_sigs_check ${space} Image Signature Checks [ enabled: ${img_sigs_enabled} ]
 isset ${github_user} && item --gap Custom Menu: ||
 isset ${github_user} && item nbxyz-custom ${space} ${github_user}'s Custom Menu ||
 isset ${menu} && set timeout 0 || set timeout 300000
@@ -116,6 +117,10 @@ goto main_menu
 iseq ${sigs_enabled} true && set sigs_enabled false || set sigs_enabled true
 goto main_menu
 
+:img_sigs_check
+iseq ${img_sigs_enabled} true && set img_sigs_enabled false || set img_sigs_enabled true
+goto main_menu
+
 :nbxyz-custom
 chain https://raw.githubusercontent.com/${github_user}/netboot.xyz-custom/master/custom.ipxe || goto error
 goto main_menu