Search in application menu (like Unity HUD)

CF bug https://bugs.launchpad.net/synapse-project/+bug/989476

A first idea could be, that when synapse is run with a different key control if would spawn with the application menu in search.
This would include application action eventually.

This would be a simple search with no actions (alternative panel).
Some shortcut could be <ctrl>+<alt>+<space> to spawn the application menu mode.
An optional shortcut would allow to switch to normal mode again.

In addition to this https://bugs.launchpad.net/synapse-project/+bug/718049
Switching between applications could be also implemented, but this seems very optional as Desktop Environments have their own performant applications switching method

To be determined :
- How to detect active window (to retrieve actions)
- How to retrieve actions

Using libindicator-appmenu would be required.

This is a start of an implementation draft, please bring any ideas you may have :)