Adds new method evictAll to IMap

Add new method evictAll to IMap
I would like to see a few more test:

- what happens when the map is empty
- when an evict all is called and later a get is done and a maploader is configured, will it be able to access the maploader again
- I don't see a test where we check that the items are really gone.
- what happens when a maploader is behind a map, but it hasn't loaded, will it first load everything and then evict everything?