Add with-connect-type to dbus signals

[muelli]

This also adds with-connect-type to the documentation.

#354
#340

CCing @gwinkenbach as the author of with-connect-type in #274

[RyuzakiKK]

I confirm that it is working as expected.
This is an example of the DevicePresenceChanged signal:

signal time=1579273753.855402 sender=:1.4447 -> destination=(null destination) serial=8 path=/org/usbguard1/Devices; interface=org.usbguard.Devices1; member=DevicePresenceChanged
   uint32 45
   uint32 3
   uint32 0
   string "allow id 0951:1642 serial "001CC870C25E4" name "DT 101 G2" hash "sVYzXusl2fPrdgo2qy" parent-hash "vawpCqjGEnZlurUwVcF9" via-port "3-1" with-interface 08:06:50 with-connect-type "hotplug""
   array [
      dict entry(
         string "hash"
         string "sVYzXusl2fPrdgo2qy"
      )
      dict entry(
         string "id"
         string "0951:1642"
      )
      dict entry(
         string "name"
         string "DT 101 G2"
      )
      dict entry(
         string "parent-hash"
         string "vawpCqjGEnZlurUwVcF9O"
      )
      dict entry(
         string "serial"
         string "001CC0EC3"
      )
      dict entry(
         string "via-port"
         string "3-1"
      )
      dict entry(
         string "with-interface"
         string "08:06:50"
      )
      dict entry(
         string "with-connect-type"
         string "hotplug"
      )
   ]

[radosroka]

Thanks!