[Feature] Add service to change action accelerators.

[mainrs]

A lot of applications offer a way to change key combinations for the available actions. A way to achieve this in drombler would be nice. Maybe some kind of OSGi service that offers an API to retrieve all Actions registered in the current application, so developer can read the metadata of them (name, id, accelerator etc). That would enable one to simply write an UI to change those values.