[Patch] Caching and notifying preferences

[michael2402]

Currently, there are many MapFrame.repaint() calls whenever properties change.

Part of this is because colors and other values are cached by each component seperately.

I added a new infrastructure that allows you to get a property and easily cache that result.

To get a property use:

new IntegerProperty("my.property", "123").get()

To cache the result, use:

prop = new IntegerProperty("my.property", "123"); // registers 123 as default value
prop.get(); // lazy get and convert to int
prop.get(); // get cached integer object

I added a new preference listener that listens to changes of one specific key to make this efficient.