Add RemoteLocation interface and abstract class

[gab1one]

A RemoteLocation is not located on the current machine. We need the
ability to set a connection timeout for such locations, to prevent them
from halting the whole program.

[imagejan]

Instead of the abstract class, could you have defined default implementations directly in the interface? Does that make any difference functionally?

[ctrueden]

@imagejan At this point I expect you have long known the answer already, but just for those curious: interfaces cannot have fields, so we could not use them to implement the setTimeout method. (For getTimeout(), returning 15000 could have been hardcoded. But it would then need to be overridden in the AbstractRemoteLocation class anyway, so it seems cleaner not to.)