Removed unused camera_position and camera_direction fields from Client. Moved ClientEnvironment::drawPostFx to ClientMap::renderPostFx -- this will make the camera management classes easier to write, as ClientMap already knows the camera position but ClientEnvironment doesn't and has to be told about it. This also eliminates the need for Client::getEnv(). Made the post effect color a content feature defined in content_mapnode.h.

Fix some texture stuff: remove item_fence.png, use fence.png, remove inexisting cactus.png from texture atlas (replace with nothing because cactus is rare)

Fixed handling of inventory in creative mode (normal inventory is not trashed anymore), fixed mese pick speed, added some forgotten stuff

- When flowing liquid starts to flow down, it stops contributing to its neighboring nodes' liquid level (possibly transforming it back to air)
- Flowing liquid turns into a source if there are at least 2 adjacent liquid source nodes
- If a new liquid flow reaches existing flowing liquid, the existing liquid is now updated properly.

- When flowing liquid starts to flow down, it stops contributing to its neighboring nodes' liquid level (possibly transforming it back to air)
- Flowing liquid turns into a source if there are at least 2 adjacent liquid source nodes
- If a new liquid flow reaches existing flowing liquid, the existing liquid is now updated properly.

New map generator added (and SQLite, messed up the commits at that time...) (import from temporary git repo)

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