Working rent feature

- PlotSignType became enum instead of abstract class. So PlotSignType2
is created and ForSale, ForRent and PlotSignType are deleted.
- Added PlotSignText class. Represents the text on a sign.
- Added TimeStringConverter to convert millisec to 1d23h59m format and
vice versa

Most changes are related to the above. Like renaming PlotSignType. And
creating/updating signs using the new PlotSignText. Other changes are
mentioned below.

- IPlotSign: Added some methods
- PlotControl: Updated method rent and buy.
- PlotData: Added method hasRenters()
- PlotListener: Updated method onSignChange
- PlotManager: Added timer for updating rent signs
- SelfServiceManager: Fixed file path issue

Next commit will rename PlotSignType2.
And there are still some important TODOs involving max rent cost. And
allowing to extend your remaining rent-time when it's below the
configured percent.
Renamed PlotSignType2 to PlotSignType without 2

This is a separate commit to avoid renaming issues with github