sdl-video: Add function to toggle fullscreen mode.
popup: Clean up options box.

Allow toggling video fullscreen mode and sound effects in options box.
Remove useless right side features.
Remove options for pathway scrolling (should be enabled always when implemented), fast map click and fast building.
Change text of messages option to be more informative.
sdl-video: Add function to free the surface backing a frame.
viewport: Add function to reinitialize landscape.

Is for example needed when a new map is loaded with different size.
mission: Move mission specifications to separate file.
game: Add functions to load mission specs and random maps.

This replaces the (badly named) game_load_random_map() which loaded mission maps with game_load_random_map() (which actually now loads a random map) and game_load_mission_map(). The code that is used by both initialization methods is moved to game_init_map().
gui: Allow GUI objects to be disabled (not receiving input).
game-init: Add GUI component for game initialization

This box is show when the game is started, and can be reopened later using F10.
Currently this box allows a new game to be started, either from a random map or from a predefined mission.
The map size or mission level can be chosen for the two game types respectively.
savegame: Fix initialization of player number when loading a save game.
Fix #72: When surrendering land fix various small potential crashes.

When calculating building influence only take into account buildings that are occupied by knights. This prevents one potential infinite recursion.
When demolishing buildings make sure that the building is not already burning. This prevents a potential crash when the non-existant flag is accessed.