Allow opening of properties draw with spacebar.

[XV-02]

Currently (dc3c4eb731bc719b4d6ea3c08ac28f5276cae092) is it possible to open the properties for a file through and alternate-click and selecting it from the context menu.

This contrasts a number of other file managers, such as Apple's "Finder", where file and property previews can be quickly displayed and hidden by tapping spacebar. This is also similar to the existing functionality of hitting enter to launch the file in the correct default application.

This should make the properties draw both more discoverable, and make previewing and navigating of certain file type - particularly images - more convenient.

[maria-komarova]

Seems to me #109 (selecting a file should open the preview) should take care of the need to use the spacebar.

[iamkartiknayak]

Alt + Enter would make more sense for opening properties of selected items in Cosmic Files. space-bar key can be used to preview supported files or show a snack-bar if it doesn't support selected format for previewing.

[jackpot51]

This is implemented