Add --version option and About dialog

[martinling]

This PR adds a --version command line option, and an About dialog to the UI.

Version information is captured at compile time with the git_version macro, so that it is possible to identify builds from non-release versions.

The About dialog includes basic package information, the BSD license text for Packetry itself, and some system information: OS, architecture and GTK library version in use.

It does not yet include copyright or license information for any dependencies.

[mossmann]

This looks great, but I get some warnings when I click the menu button:

(packetry:95267): Gtk-CRITICAL **: 15:54:33.990: _gtk_css_corner_value_get_x: assertion 'corner->class == &GTK_CSS_VALUE_CORNER' failed

(packetry:95267): Gtk-CRITICAL **: 15:54:33.990: _gtk_css_corner_value_get_y: assertion 'corner->class == &GTK_CSS_VALUE_CORNER' failed

[mossmann]

I'm on:

OS: linux
Architecture: x86_64
GTK version: 4.10.4

I think this is a GTK bug fixed in: https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/6092

[martinling]

I'm on 4.12.5 and I don't see those messages. I think we can assume it's not our fault.

[mossmann]

I realized just too late that there is an issue with this when building outside a git repository:

   Compiling packetry v0.1.0 (/tmp/packetry)
error: git describe exited with status 128: fatal: not a git repository (or any of the parent directories): .git
   --> src/ui.rs:998:31
    |
998 |     const GIT_VERSION: &str = git_version::git_version!();
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: this error originates in the macro `git_version::git_version` (in Nightly builds, run with -Z macro-backtrace for more info)

error: git describe exited with status 128: fatal: not a git repository (or any of the parent directories): .git
  --> src/main.rs:56:41
   |
56 |         println!("Packetry version {}", git_version::git_version!())
   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the macro `git_version::git_version` (in Nightly builds, run with -Z macro-backtrace for more info)

error: could not compile `packetry` (bin "packetry") due to 2 previous errors

This would happen if someone downloads a "source code" archive from a release on GitHub or (as some distro packagers are known to do) checks out a tag from the repo but omits the .git directory. We solve this problem in HackRF by including the a hard-coded version number within the repo and falling back to the hard-coded number if the git method fails.