Draft: Add intent-apps spec, based on the mime-apps spec.

HTML output at http://andyholmes.ca/public/intent-apps/intent-apps-spec.html

Overview of Tasks (as of last edit):

1. Platform Issues
   • Currently, e.g. org.freedesktop.FileManager1 is started by calling an interface method, which should happen in platform libraries like GLib/KDE.

   • David Faure commented: Dolphin isn't DBus-activatable as org.kde.dolphin because it's not a "unique application", it registers as org.kde.dolphin-$PID. The first launched Dolphin registers under the additional name org.freedesktop.FileManager1, so DBus-activating org.freedesktop.FileManager1 does work, but not the above strategy.

   • Comment thread 1/2
   • Comment thread 2/2
2. File Format issues
   • Support for .ini files may need minor adjustments. Currently localized key parts (e.g. en_US.UTF-8@latin in SomeKey[en_US.UTF-8@latin]=value) only allow characters from lang codes. We would require the characters for mime-types (/, +), probably added to the Desktop Entry spec format description
   • This may be problematic if a Flatpak'd .desktop file is exported to a host that doesn't support the new format
3. D-Bus Policy vs. Mechanism
   • Option 1: a portal can provide the names and resolution can happen portal-side (best current choice?)
   • Option 2: intent-apps.list can be bind-mounted into sandboxes
   • Option 3: Containers1 interface
4. Specification Ambiguities
   • Delineate "most preferred" and "default"
   • Define the format for intent names (domain owner, formalize org.freedesktop.*, or allow x-org.freedesktop.*?)
   • Intents don't have to be D-Bus services, but should follow versioning conventions