build: Various meson related improvements

Merged Iñigo Martínez requested to merge inigomartinez/gtranslator:meson-review into master

meson build system has received several improvements. The list of improvements is as follows:

  • The prefix used for different variables has been changed to gtr.
  • Indentation has been changed to that most commonly used.
  • Unnecessary files have been removed.
  • GTK documentation generation has been fixed.
  • schemadir location is now checked from GIO's pkg-config file when available.
  • profile has been removed and debug builds are considered now development builds.
  • documentation option has been renamed to gtk_doc to be consistent with different GNOME packages using the same option.
  • meson post install script does not build paths based on installation prefix because these might vary.

Merge request reports