UI and gameplay updates

UI changes:

- Main menu got an animated background image scrolling that fades in and out, so it feels less "empty". Currently 3 images are going around.

- Ingame Controls and Gameplay info got 1-1 show/hide buttons, so they no longer overlap the gameplay area unnecessarily. These are temporary panels, but they will not be removed as long as the ingame tutorial is not implemented.

- Game speed contol got some green coloring to show which game speed is actually selected. The design will change in the future, but for now it is really helpful to see how fast the gameplay is going.

Gameplay changes:

- Turrets now search for an opponent when they dont have any, so the pace of their actions are more fluent.

- Some small bugfixes were made regarding the turret filler drones, but there are still problems with them so the 0.3 version is still not ready for release.