Update to snapd v2.26.3 and snapd-glib v1.12.

Some of the upstream snapd v2.26.3 software highlights (from the Snappy team):

• support tab-completion in snaps, i.e a snap can ship a bash completion script and it will get exported to the users shell
• new snap whoami command
• new snap refresh --time option that displays information about refresh settings
• new snap tasks --last={refresh,install,remove,connect,disconnect,configure,try} option
• Improve snap info output
• Improve tab completion for interfaces
• Mediate netlink sockets via seccomp
• Go 1.8 fixes
• Interface API improvements
• new interfaces: random, network-status, online-account-service, storage-framework
• Interface improvements: browser-support, locale-control, dbus

From snapd 2.25:

• Improved aliases implementation, details in https://forum.snapcraft.io/t/improving-the-aliases-implementation/18
• Improved channels support (tracks), see https://forum.snapcraft.io/t/channels-2-0-implementation/156
• Per-revision snapshots of the snap configuration refresh schedule support, see https://forum.snapcraft.io/t/refresh-schedule-via-core-config/434
• Cross distro improvements (Xauthority handling, etc.)
• Test improvements (more spread tests)
• More fine-grained seccomp support for ioctl and quotactl
• Download robustness improvements (auto retry on hashsum and RST issues)
• New snap tasks command
• Speedup for device key generation on Pi 2 and Pi 3
• New interfaces: media-hub, kubernetes-support
• Interface improvements

Highlights for snapd-glib v1.12 since v1.10:

• New API:
  • snapd_client_install2_async
  • snapd_client_install2_finish
  • snapd_client_install2_sync
  • snapd_system_information_get_binaries_directory
  • snapd_system_information_get_kernel_version
  • snapd_system_information_get_mount_directory
• Fix calls not working inside threads.

• Fix reference counting error when calling snapd_client_get_interfaces and snapd_client_create_user.

• Deprecated API:

  • snapd_client_install_async
  • snapd_client_install_finish
  • snapd_client_install_sync

Packaging specific improvements:

• Final removal of snapd will trigger removal of all Snappy content