feat(build): add nix-shell support

Add a metadata file and build rules to build and test from a development
shell provided by the Nix package manager.

.gitignore

@@ -16,6 +16,7 @@ qtox
 build-*-Release
 build-*-Profile
 build-*-Debug
+.qtox-wrapped
 
 # Folders
 _[Bb]uild*/

CMakeLists.txt

@@ -714,3 +714,12 @@ target_link_libraries(${PROJECT_NAME}
 
 include(Testing)
 include(Installation)
+
+if (DEFINED ENV{IN_NIX_SHELL})
+  # the qtox binary must be "wrapped" to find the Qt platform plugin
+  # and other dependencies at runtime
+  add_custom_command(
+    TARGET ${PROJECT_NAME}
+    POST_BUILD
+    COMMAND nix-shell --run "wrapQtApp ${PROJECT_NAME}")
+endif()

shell.nix

@@ -0,0 +1,2 @@
+{ pkgs ? import <nixpkgs> { } }:
+pkgs.mkShell { inputsFrom = with pkgs; [ qtox ]; }