Fix #37 : Add a new key binding CTRL+R which resolve, load and set the TP

This commit adds a new command + key binding to set the current
.targetplatform file as the current targetplatform. It wraps the .target
generation, the target resolving and reload in a single job, with no
need for opening the preference page or the .target editor.

This command is also available right-clicking on a .targetplatform file
(if only one is selected).