Moved some mapnode content stuff from mapnode.{h,cpp} and digging property stuff from material.cpp to content_mapnode.{h,cpp}

Added an experimental "far view" thing. Doesn't work exactly like it should and not suitable for real use yet, and might never be.

Merged CiaranG's fence graphic updates (ugh, well, it worked, i guess, kind of.) This commit should also get rid of multiple heads on the server.

Reduced server CPU usage on NodeMetadata step()s. Also furnace now cooks while no players are near it.

Updated licenses of CiaranG's contributions to be in line with the new contribution policy and added a TODO note to server.cpp

...and added support for simple time usage profiling in the last one.

Note: can't test this properly yet - may be fixes to follow

--HG--
extra : rebase_source : e2d41621018f886d340c7847b29240042d4412ac

--HG--
extra : rebase_source : 762df9f579bc0ba917986f68ac459fa89fcce794